History for Characters/TheBindingOfIsaac

[[/index]]

!Plot-relevant characters

[[folder:Isaac]]
!!Isaac
[[quoteright:248:https://static.tvtropes.org/pmwiki/pub/images/isaacopening.png]]
A little boy who flees into the basement of his house to escape from a mother who wants to kill him, and must fight for his life against a never-ending assortment of demons and mutants. Beating the game in certain ways or collecting certain items unlocks variations of Isaac with their own unique attributes.
%%If you don't agree, please take it to the discussion page. It's pretty clear once you beat the game the first time that Isaac is just wearing accessories. WordOfGod also confirmed this is true.

For tropes related to Isaac and his alter-egos in gameplay, scroll down to the section on player characters. For tropes related to Isaac as the boss enemy of the Cathedral, scroll down to the section on major bosses.
----
* AllOfTheOtherReindeer: In addition to having an abusive mother and a DisappearedDad, flashbacks also show him suffering [[KidsAreCruel bullying from other kids]], such as having [[PantsPullingPrank his pants pulled down]] while trying to impress a girl, getting crapped on (literally), getting knocked down by a dodgeball, and being made fun of for wearing a wig.
* BreakTheCutie: The entire premise of the game is one for him.
* ChildrenForcedToKill: Isaac has to fight and kill plenty of enemies just to survive, up to and including his own religiously psychotic mother. [[spoiler:Or so it seems]].
* CreateYourOwnVillain: Well, antagonist. Isaac would never have been forced to kill his own mother if she hadn't snapped and tried to sacrifice him in the first place. [[spoiler:This gains some ''very'' interesting implications at the true ending of ''Rebirth'', where it's revealed that Isaac becomes a demon or the AntiChrist inside the Chest. Did Isaac have darkness inside him all along, or did he [[ThenLetMeBeEvil decide to become evil]] after all the horror that he went through?]]
** As it turns out, [[spoiler:this trope is played ''literally'', with the revelation that the entire game is Isaac's DyingDream]].
* {{Crossdresser}}: A few between-level cutscenes show him wearing a dress or a wig, not to mention the fact that all female "player characters" are him crossdressing.
* DarkAndTroubledPast: The horrible memories of things that Isaac suffered through are relived in level loading screens. In one ending, the photograph montage of Isaac's past leaves a lot of interpretation as to what happened to his family, namely what happened to his father (who likely left, went missing, or died). [[spoiler:The final ending of ''Afterbirth+'' confirms that he left, and this point is reiterated in ''The Legend of Bum-bo''[='=]s main ending.]]
* DeadAllAlong: [[spoiler:After beating It Lives for the tenth time and unlocking Ending 10, Isaac comes across his corpse stuffed into a chest. At least one interpretation of this involves Isaac having been dead the whole time. The next three endings explore the events leading up to his death in reverse chronological order, first showing him willingly [[DrivenToSuicide locking himself in the chest]], then showing his self-loathing which led to this, and finally showing his [[DarkAndTroubledPast tragic backstory]] through a heartbreaking PhotoMontage. After beating Hush in ''Afterbirth'', if you end your run there, not going on to Cathedral or Sheol, you get Ending 17, which outright confirms it, as Mom opens the Chest to find Isaac's skeletal remains.]] Ending 20, the true ending to the game, reveals that [[spoiler:he has long since been DrivenToSuicide and that none of the game is even happening]].
* DrivenToSuicide: Isaac hangs himself upon finding Transcendence (a noose) in Ending 2. [[spoiler:This is PlayedForDrama in the final few endings: After we see that Isaac has been DeadAllAlong in the tenth ending, we are shown him willingly entering the chest himself in Endings 12 and 13, and the twentieth ending reveals that it was due to his self-loathing as he sees himself as a demon after his family breaks apart.]]
* DyingDream: [[spoiler:Ending 20 reveals that the whole game is this, including the thought of his mother attempting to kill him.]]
* EnemyWithout: [[spoiler:There are four variations of Isaac that serve as bosses: It Lives, the boss of Womb II confirmed to be Isaac as an embryo; normal Issac, the boss of Cathedral; Hush, the boss of the Blue Womb and a suffocating version of Isaac; and finally ???, boss of the Chest and Isaac after suffocating to death.]]
* FullFrontalAssault: Unless an item is picked up, Isaac is battling the monsters of the basement stark naked.
* HilariouslyAbusiveChildhood: Many of the level intermission vignettes have Isaac getting picked on by kids, being dressed in drag, getting poop as a birthday gift, [[ArsonMurderAndJaywalking realizing he has no toilet paper while he's on the toilet]], and the list goes on. And that's not even speaking of some of the items -- the Wooden Spoon gives you scars, implying Isaac was ''beaten'' with it by his mom, the Belt is [[DontMakeMeTakeMyBeltOff self-explanatory]], and many of the food items [[IAteWhat aren't exactly fit for human consumption]].
* IronicName: "Isaac" means "he laughed" or "he who laughs." [[TheWoobie Not much laughing occurs]]. [[OcularGushers Quite the opposite, really.]] [[invoked]]
** Although it was based off the biblical story. See MeaningfulName below.
* ItsAllMyFault: The ending you get for beating the Chest seems to imply that [[spoiler:the cause of Isaac's self-loathing is because he blames himself for his father leaving. His mother seems to blame him as well]]. Ending 20 eventually reveals that [[spoiler:he does blame himself, and this is what ultimately causes him to be DrivenToSuicide]].
* KindheartedCatLover: Whenever the player gets a GameOver, Isaac usually states in the diary that he will give what he collected to his pet cat, Guppy.
* MadnessMantra: [[spoiler:BAD BAD BAD BAD I'M THE DEVIL...]]
* TheMentallyDisturbed: With all said and done about the new endings in ''Afterbirth+'' comes the spine-chilling conclusion that, [[spoiler:by experiencing losses too grave for his age, together with the outcast status forcefully pinned by other children, this whole game can be interpreted as Isaac's slow descent into schizophrenia. Small wonder that the game seems to run on BlackHumor and [[WidgetSeries widgettiness]] now, huh...?]]
* MrImagination: ''Horribly'' deconstructed. [[spoiler:Isaac has the vivid imagination expected of a child his age, but his troubled childhood and self-loathing lead to his imagination going to very, very strange and dark places. Even as he suffocates inside his toy chest.]]
* NakedOnArrival: He is naked throughout almost the entire game.
* SanitySlippage: [[spoiler:Isaac is slowly going insane the longer he is in the chest, as shown by the final level and boss being amalgams of previous levels and bosses.]]
* SuddenlyVoiced: [[spoiler:One of the main endings of ''The Legend of Bum-bo'']] features Isaac's first spoken words in the series, [[spoiler:begging Mom to leave his cardboard toys alone]].
--> “[[spoiler:No, no, mama, please!]]"
* ThenLetMeBeEvil: [[spoiler:It is strongly implied that at the ending of ''Rebirth'', Isaac becomes a demon or TheAntichrist in order to deal with all the horror he went through, up to and including his mother.]] [[spoiler:Ultimately subverted, as this is how he sees himself, for, in his own mind, being the reason his father "left forever".]]
* TroubledFetalPosition: Isaac's signature pose.
* TroublingUnchildlikeBehavior: With [[spoiler: the game's reveal that it was just all in Isaac's head]], one could wonder what exactly is ''going on'' inside this kid's head, with the game's vast amount of BodyHorror and violence. Even the items leave disturbing implications, with the item pool including a gimp mask, a razor blade for self-harm, a suicide vest, drug needles, ''literal cancer'', ect. Just ''what'' kind of stuff has Isaac [[HarmfulToMinors been exposed to]]?!
* VagueAge: Fans have theorized Isaac being from a toddler to at most seven years old. He's at least old enough to walk and go to school, and ''The Legend of Bumbo'' reveals that he can [[spoiler: talk]]. Edmund also tentatively HandWaved in a tweet that Isaac is five.
* WalkingSpoiler: Due to the endings revealing more and more of what is actually going on between him and his family, it's only a given.

[[/folder]]

[[folder:Mom/Magdalene O. Moriah]]
!!Mom
[[quoteright:350:https://static.tvtropes.org/pmwiki/pub/images/momopening.png]]
->Debut: ''The Binding of Isaac''

[[ExactlyWhatItSaysOnTheTin Isaac's mother.]] A devoutly religious woman who, in a fit of rage/insanity/fanaticism/[[WildMassGuessing whatever you think it is]], tries to kill Isaac, forcing him to flee to the basement.

For tropes relating to Mom as a boss enemy, scroll down to the section on major bosses.
----
* {{Abusive Parent|s}}: Takes away all her son's stuff, locks him in his room, and then tries to ''kill him''. Convinced by God to do so or not, that's all the evidence you need. However, the true ending reveals that [[spoiler:this is possibly a subversion, depending on whether you see the between-level cutscenes as being canon or not]].
* TheBadGuyWins: [[spoiler:It's revealed that Isaac suffocated to death while inside the chest. She wanted Isaac to die because of an [[ThroughTheEyesOfMadness (alleged)]] order from God, do the math. However, subsequent endings reveal that Isaac locked ''himself'' in the Chest ''before'' the events of the game, and ''Afterbirth+'' reveals that she was never intending to kill him and that Isaac saw himself as a demon and the cause of his family breaking apart, making this a cruel subversion.]]
* BigBad: The game is kickstarted by her attempting to murder her son. [[spoiler:Ultimately subverted; the only evidence of this comes from Isaac's own mind, which is unreliable at best.]]
* TheExtremistWasRight: She's a religious fanatic that appears to think that she's on a mission from God, which is clearly not the case. [[spoiler:At least until the end of ''Rebirth'', strongly implying that Isaac either was or now is a demon. If you subscribe to the "just insane" theory, then she's RightForTheWrongReasons.]]
** Subverted as of Ending 20: [[spoiler:Isaac made up the story, possibly to explain why she was acting so abusive without taking the blame off of himself.]]
* TheFaceless: While you see her face in Isaac's doodles, the actual Mom gets the [[Series/HomeImprovement Wilson]] treatment in that you never get to see her entire face at once, only a single eye, or the lower half of it if you use Mom's Bra.
* {{Foreshadowing}}: The opening pretty much implies she's reenacting the role of Abraham in Yahweh's covenant. [[spoiler:Which means, in case you're not a Bible buff, that this whole act is doomed to ''fail'' if she plays it as intended, as this time there's no angel to stop her and save her son's life.]]
* TheFundamentalist: She's heavily Christian, and her hearing the voice of God is what kicks off the plot.
* {{Gonk}}: To grotesque, nauseating levels. [[spoiler:Subverted, as the new endings hint at the possibility that [[ThroughTheEyesOfMadness this is how Isaac's addled mind interprets her appearance]].]]
* HiddenDepths:
** [[spoiler:Ending 13 [[note]]14 in ''Rebirth''[[/note]] reveals that she used to be completely sane, and the caring and loving mother of a fully-functional family. However, as the family fell apart, so did her sanity.]]
** [[spoiler:Endings 15 and 17 suggest that in the end, she might be at least ''somewhat'' concerned about her son's well-being.]]
** [[spoiler:The final ending, 20, confirms that Mom is nowhere near the psycho that Isaac's brain made her out to be, and never intended to kill him at all. She's seen weeping in front of the television after his father leaves the family.]]
* KnifeNut: She's holding her knife in almost every cutscene she appears in, and you can unlock said knife as a usable weapon in-game.
* MaybeMagicMaybeMundane: Is she really hearing the voice of God, or is she just completely insane? The best we get from [=McMillen=] is him [[https://upvoted.com/2015/10/03/edmund-mcmillen-binding-of-isaac-profile/ stating]]:
--> “It was never implied that [Mom's] insane. And if you're going by the Bible and you believe all the stories, [[BeliefMakesYouStupid then why wouldn't you think that it's possible now for that stuff to happen?]]”
* NoNameGiven: Unlike Isaac, even her first name is unknown in the game prior. According to the [[https://twitter.com/edmundmcmillen/status/1027346682227257351 'Credit Card' card from Binding of Isaac: Four Souls]], her full name is [[FunWithAcronyms Magdalene O. Moriah.]] [[MeaningfulName "Moriah" is the location where the biblical Isaac was to be sacrificed.]]
* OffingTheOffspring: Her ultimate goal [[spoiler:in Isaac's DyingDream]].
* OneBadMother: Bonus points for actually being the main character's mother.
* SuddenlyVoiced: [[spoiler:One of the main endings of ''The Legend of Bum-bo'']] features the real Mom speaking full sentences for the first time.
--> "[[spoiler:Isaac... who were you talking to?]]"
[[/folder]]

[[folder:God/The "Voice From Above"]]

In the opening narration, a voice from above claims to be God to Isaac's mother and instructs her to kill him.

* AmbiguousSituation: Is it ''really'' God's voice, Satan's, or someone else's? One of the between-floors clips added in ''Afterbirth'' shows the scene of Mom hearing the voice from above, except the camera, moves up to show the Lost speaking. [[spoiler:The final ending implies that there was no "voice" to begin with, and Mom was never trying to kill Isaac.]]
* TheGhost: Despite playing a part in the game's initial story, God never actually appears in-game. Even the holy counterpart to Devil Rooms are Angel Rooms, which have Uriel and Gabriel in them instead. The only item outright said to be God-related[[note]]unless one counts "God's Flesh," but that is a slang term for psychedelic mushrooms[[/note]] is Godhead, which gives Isaac a third eye and a glow on his head.
* SecretTestOfCharacter: The Epilogue suggests this was the case with Mom, as the narrator describes her death as "God intervened" despite supposedly ordering her to kill Isaac in the first place.
* ThirdEye: Suggested with the Godhead item, as it gives Isaac a third eye and "God tears." If the item is considered as ''adding'' a God-like eye to Isaac's head, since Isaac's "normal" eyes are unchanged and the item itself just shows one eye in a triangle, then this game's depiction of God might have only one eye instead.
* TheUnfought: Isaac never encounters God in-game. Even when going to a cathedral, the boss of that is Isaac himself, and the floor after that is not another holy location so much as it is a chest where Isaac's post-mortem counterpart lies (and where Isaac must confront reality).

[[/folder]]

[[folder:Dad]]

Isaac's father, who is not part of the family by the time the game takes place.

* AbusiveParents: [[spoiler:Some of the items in the game (bad/rotten food for "breakfast/lunch/dinner," the Belt and Spoon being speed boosters, etc) suggest that Isaac has at least one abusive parent. Ending 20 suggests that it may or may not be Mom, which would logically point to Dad if that is the case. Either way, collecting the passive item Dad's Lost Coin makes poor Isaac look ''[[https://gamepedia.cursecdn.com/bindingofisaacre_gamepedia/9/96/Dad%27s_Lost_Coin_App.png miserable.]]]]''
** [[spoiler:However, ''The Legend of Bum-bo'' implies in its final ending that Dad was not the abusive one. He gave well-intentioned advice to Isaac about fueling his imagination to help cope with reality, and claimed that he will always be with Isaac in spirit. That said, he's also the one who made the cardboard toys Isaac plays with, which are... mature, disturbing, and grotesque, to say the least. Certainly not appropriate for a five-year old to play with.]]
* AlcoholicParent: [[https://i.gyazo.com/7719e028341e1e6bb1afd49d4994b855.png The Dad's Lost Coin card]] in ''The Binding of Isaac: Four Souls'' is an Alcoholics Anonymous chip.
* DisappearedDad: Right from the beginning of the game, the intro states that Isaac lives alone with his mother. [[spoiler:The final ending implies that something happened which caused him to leave in anger and drove him away from Mom, and by beating the BossRush as The Forgotten, you unlock the ''Divorce Papers''. Notably, the Dad's Key item lets Isaac open any door [[note]]even the one leading to Mega Satan[[/note]] — in other words, leave the given room he's in.]]
* TheGhost: Justified considering the game's setting. He's already out of the family, and Isaac instead wanders the Basement fending off demons. [[spoiler:However, even as it becomes clear that the gameplay is set in a DyingDream, Dad himself is never directly encountered.]]
* GreaterScopeVillain: Subverted; [[spoiler:he is mostly responsible for the deranged setting and monsters that Isaac encounters, but he only created them in the hopes that Isaac would learn to use his own imagination as a coping mechanism]].
* UnwittingInstigatorOfDoom: [[spoiler:''The Legend of Bum-bo'' reveals that he (at least partially) created the "world" that both it and ''The Binding of Isaac'' take place in, with the intention of teaching Isaac to rely on his own creativity in order to deal with the stresses of reality. Unfortunately, Isaac becomes too delusional with the mental world he and Dad formed together, and ultimately chooses to commit suicide instead of moving on with his life.]]
* WalkingSpoiler: Plays a part in the game's overall lore, but is not really hinted at doing so until around unlocking the Polaroid/Negative, which takes over a dozen playthroughs (assuming no skipping involved with items, buttons, or Error/Black Market rooms generating trap doors). Or by going through Hush and Delirium and seeing Ending 20, since it is possible yet difficult for newer players to beat that path before unlocking either photograph. ''The Legend of Bum-bo'' takes it even further by revealing Dad's true significance in the setting of both games.

[[/folder]]
[[folder: Bumbo]]
!!Bum-bo
A naked baby who lives with his trash. He's the protagonist of "The Legend of Bum-bo," when a monster steals his precious golden coin.

* BerserkButton: He’s ''very'' attached to his single coin, so when a monster takes it away, he does not hesitate in following it and beating up any other monster who stands in his way.
* BoisterousBruiser: He’s a loud, brave bum who likes to punch his enemies into mush. It’s especially evident whenever he kills a boss, letting out a triumphant “OOOOH YEAH!” as it explodes into gibs.
* BreakoutCharacter: Originally a familiar for Isaac to recruit, Bum-bo saw a considerable rise in popularity before starring in his own game.
* ContrastingSequelMainCharacter: Isaac is a scared child who enters the unknown depths to escape from his mother, and primarily attacks with ranged tears. Bum-bo, however, is brave and cheerful, willingly follows a monster into the unknown depths after it takes his coin, and prefers to smash enemies with his fists.
* TheGambler: Despite his obsession with the coin, one ending features him feeding it to a slot machine (though he hesitates for a long while before doing so).
* MagikarpPower: How he works as a familiar in ''The Binding of Isaac''. Bumbo starts out doing nothing but taking money (which makes him even worse than Bum Friend, who at least gives you stuff in return), but as he collects more coins, he gains more abilities. Once he's fully powered up, Bumbo is easily the strongest familiar in the game, capable of spitting out tons of items and single-handedly murdering most bosses.
* SpellMyNameWithAnS: As a familiar in ''Isaac'', his name is spelled as "Bumbo" without the hyphen. Also EarlyInstallmentWeirdness as the hyphen was added after he got his own game.
* ThirdPersonPerson: He mostly speaks this way whenever he’s narrating a cutscene. [[spoiler:This may be because "Bum-bo" is in fact Isaac's dad, narrating the setting of the world Isaac would escape to if he ever becomes too stressed.]]
* WhamLine: In the true ending, Bum-bo talks about making his "kingdom" and expanding it, filling it with adventure, [[spoiler:until his voice suddenly changes, and reveals that his kingdom was made for Isaac and that "Bum-bo" was in fact his father, who did it all to help Isaac escape the stresses of reality]].
[[/folder]]

!Playable Characters

[[folder:In General]]
* {{Acrofatic}}: Several items make your character fatter, and most don't negatively impact speed. Combine these with items that increase your speed and you have this trope.
* AmazingTechnicolorPopulation: Stat-boosting pills change the character's color (Green for Luck, red for Health, etc), as do a few of the items. Most demon-related items turn the character into a black-skinned demonic hybrid, and Anti-Gravity turns them blue, for two examples.
* BadassAdorable: He's still a child at the end of the day.
* BerserkerTears: Unlike most examples, he fights ''by'' crying.
* BlessedWithSuck: Guppy's Tail makes you find golden treasure chests more often. This comes at the expense of keys needed to open those chests, though if you're lucky, the chests cough them up. [[CursedWithAwesome Works wonders with items that can create keys, such as the Skeleton Key or a Flat Penny]]. This is made potentially worse or better with The Left Hand trinket that changes all chests to Red Chests. They don't require a key to open, but half or more of the things that come out of a red chest are not something you want (including enemies and troll bombs).
* BlondeBrunetteRedhead: The three female playable characters: Magdalene (blonde), Eve (brunette), and Lilith (redhead).
* BodyHorror: A ''lot'' of items mutilate or mutate the character in some horrific way. For example, Chemical Peel causes half of the character's face to be torn off, Growth Hormones causes hideous lumps to form over the character's body, Stem Cells causes a fetus to grow on the side of the character's head, The Parasite burrows into the character's skull and dyes their tears a disgusting orange-brown, and 8 Inch Nails has two nails shoved [[EyeScream in each of of the character's eyes]].
* BringMyBrownPants: Entering a room with half a heart makes the player leave yellow urine stains on the floor (unless playing as Eve, whose stains are red instead).
* BulletHell: It's possible to get a character that shoots a four-way bullet spread at the speed of a machine gun with additional single shots from the other three cardinal directions. And honestly, that's a pretty tame possibility.
* DarkIsNotEvil: An Isaac with a lot of Devil items is still just looking to survive.
* DidYouJustPunchOutCthulhu: Isaac can tear apart any number of bosses over the course of the game, including [[spoiler:''Satan'']].
* EmpoweredBadassNormal: No matter which version you choose, you'll inevitably turn him into a supernatural being in the process of beating the game.
* FantasyCharacterClasses: The characters are based on archetypal RPG classes (with a few exceptions).
** The Hero/Balanced/Fighter: [[JackOfAllStats Isaac]]
** The Cleric: [[WhiteMage Magdalene]]
** The Thief: [[FragileSpeedster Cain]]
** The Mage: [[SquishyWizard Judas]]
** The Druid: [[GlassCannon Eve]]
** TheBerserker: [[BarbarianHero Samson]]
** The Dark Knight: [[CloseRangeCombatant Azazel]]
** The Theurgist: [[TouchedByVorlons Lazarus]]
** The Summoner: [[SummonMagic Lilith]]
** TheGambler: [[MechanicallyUnusualClass Keeper]] (only after unlocking Wooden Nickel)
** The Blue Mage: [[PowerCopying Apollyon]]
** The Battle Mage: [[TheDividual The Forgotten]]
* FlashOfPain: His sprite blinks when he takes damage.
* {{Flight}}: Plenty of items, both permanent and temporary. You can become an angel, a demon, an angelic ghost, a demonic ghost, a floating head, and a cat (which somehow flies). All of these let you pass through rocks and over pits, as well as over hazards like creep and spikes.
* FullFrontalAssault: Before the events of the game, his clothes were taken away from him as part of Mom's attempts to remove the evil around him. In most playthroughs, he fights his way through monsters naked.
* {{Gasshole}}: Certain items can invoke this in the player, such as Butt Penny, Mysterious Candy, the "Bad Gas" pill, and pretty much all the bean items. Also combines with {{Fartillery}} if the item is used for combat.
* GoodWingsEvilWings: Both are possible, though not at the same time — Angel items for the "good" variant, and Devil items for the "evil" ones.
* HeWhoFightsMonsters: As he fights through deformed monsters and demons, he will end up getting a lot of things that make him just like those deformed monsters and demons.
* ImprobableWeaponUser: Mainly his own tears. With appropriate items, he can upgrade to teeth, urine, and explosive vomit, among other things.
* ItemGet: Holds up new items — [[TooDumbToLive even in battle]]. You're not invincible when that happens, either.
* KindheartedCatLover:
** Isaac seems to adore Guppy the cat the most out of his (deceased) pets.
** He seemed to also like Max (Cricket in ''Rebirth'') second most out of the pets, or possibly equally to Guppy because Max's head makes him cry hardest of all items.
** There is also Tammy, who, although she doesn't evoke as strong a response as Guppy, will still make Isaac cry more than normal, translating into a 360 shot.
* MeaningfulName: Most of the playable characters' names relate to Bible stories, with Isaac's name relating to the ''Binding of Isaac'' story the game is based on. ''Four Souls'' suggests his last name is Moriah, the mountain from the same story.
* NoNameGiven: His surname is never known in-game. When ''Four Souls'' [[https://twitter.com/edmundmcmillen/status/1027346682227257351 confirmed Mom's name,]] his last name would logically be Moriah — the mountain in the Biblical story of Isaac. [[spoiler:The only hazy part is whether or not that's Mom's maiden name, and whether she and/or Isaac have it after Dad left.]]
* OcularGushers: Most playable characters have a constant stream of tears running down their faces. After all, they are Isaac's main weapon.
* PaperThinDisguise: It is strongly implied in-game (and confirmed by WordOfGod) that all the characters are just Isaac putting on a wig, eyepatch, hat, etc.
* SecretCharacter: There are numerous transformations available, which are activated by collecting three items of a particular set (flies, cats, etc.), after which the transformation effects are permanent for that run. The three items only need to have been held once, even if replaced (for Active items) or rerolled (for passive ones). The original had only Guppy, while ''Rebirth'' added Lord of the Flies. ''Afterbirth'' added eight more, and ''Afterbirth+'' added another three.
** Guppy, activated by picking up three Guppy items, transforms the player character into Isaac's pet cat. Doing so unlocks a new item (the first time), gives you flight, and applies a buffed version of the Mulligan that spawns a fly upon every hit.
** Lord of the Flies/Beelzebub, activated by picking up three fly-related items, turns the player into a humanoid fly, grants flight, and turns all regular flies into kamikaze flies.
** Seraphim, activated by picking up three holy items, gives Isaac angel wings for flight and three soul hearts.
** Bob, activated by picking up three Bob items, turns Isaac green and causes him to release a trail of green creep where he walks.
** Leviathan, activated by picking up three satanic items, transforms Isaac into a mini-Cthulhu, granting flight and three black hearts.
** Spun, activated by picking up three syringe items, makes Isaac buff, gives a damage increase, and spawns a random pill.
** Yes Mother, activated by collecting three Mom items, dresses Isaac as Mom and creates a copy of Mom's knife which trails behind the player (not as a familiar, but as an inverted copy of the knife controlled by movement).
** Fun Guy, activated by picking up three mushroom items, gives Isaac a mushroom hat and adds a heart container.
** Oh Crap, activated by picking up Flush, The Poop, and E. Coli, turns Isaac into a walking poop and heals him by half a heart every time a poop is destroyed.
** Super Bum, activated by picking up the three Bums, combines the three Bums into a single Bum that grabs every pickup in the room and drops twice as many in return.
** Conjoined, activated by picking up three of a certain set of familiars (Brother Bobby, Harlequin Baby, Headless Baby, Little Steven, Mongo Baby, Rotten Baby, and Sister Maggy), causes Isaac to grow two tumors on either side of his face, giving him permanent diagonal tears similar to The Wiz, at the cost of slightly lowered tears and damage.
** Bookworm, activated by picking up three book items, gives Isaac a monocle and lets him occasionally shoot from both eyes at once.
** Spider Baby, activated by picking up three spider items, gives Isaac a spider familiar that applies random status effects to enemies.
** Adult, activated by taking three Puberty pills, makes Isaac's voice deeper and gives him a scruffy beard and a heart container.
** Stompy, activated by increasing in size three times through any combination of Leo, Magic Mushroom, and the One Makes You Larger pill, causes Isaac to create dust clouds when walking and lets him occasionally release rock waves when taking damage.
* SwissArmyTears: As a weapon! With the appropriate items, Isaac can get poison tears, homing tears, fear-inducing tears, spectral tears, magnetic tears, petrifying tears, exploding fire tears, tears that summon beams of light from Heaven, or any combination thereof. And that's not even a complete list.
* TearsOfFear: Pretty understandable given the situation he's in.
* ThrowDownTheBomblet: The bombs he can carry around are pretty good for killing things as well.
* TookALevelInBadass: Throughout the game, if the right items are acquired, Isaac starts the game as a crying child and can potentially end it as a flying demon that can demolish bosses in seconds with giant lasers.
* WingedHumanoid: Possible with certain items.
[[/folder]]

[[folder:Isaac]]
!!Isaac
[[quoteright:112:https://static.tvtropes.org/pmwiki/pub/images/isaac.png]]
->Debut: ''The Binding of Isaac''
Named after the biblical son of Abraham, is playable from the start and has no defining accessories. [[WordOfGod According to Edmund McMillen]], he represents the fighter class of traditional games and begins with no items.
----
* BadassNormal: He's the only playable character that starts off without any sort of items or supernatural assistance. Even [[spoiler:the D6]] is merely [[spoiler:a six-sided dice]].
* BaldOfAwesome: Being a young child, he has no hair normally. It doesn't hinder him at all from kicking Satan's ass.
* BoringButPractical: In both the Flash and ''Rebirth'' versions, he always starts with a single bomb. It seems like nothing much, but it guarantees you'll be able to blow up a marked rock (and get DMG up and/or Soul Hearts) should you encounter one, or take a shot at finding a secret room.
* HeartIsAnAwesomePower: His unlockable starting item is merely [[spoiler:a six-sided dice]]. Many players agree that it is among the best starting items in the game regardless, since it rerolls any pedestal items in the room into potentially better ones.
* HeWhoFightsMonsters: [[spoiler:Isaac ''himself'' is an alternate [[strike:TrueFinalBoss]] [[DiscOneFinalBoss Disc Three Final Boss]] that can be fought instead of Satan. More details below.]]
* JackOfAllStats: Average in all stats except for having 3 starting hearts.
* LuckManipulationMechanic: [[spoiler:[[MundaneMadeAwesome The all-mighty D6 dice!]] An activated item capable of transmuting any pedestal item into a different one.]]
* MagikarpPower: At first, he'll be outclassed by almost every other character you unlock, as they are more durable, faster, more powerful, and/or more useful than him. But if you take your time and persevere in order to [[spoiler:unlock his starting item]], he'll become the most versatile and flexible of them all.
* MasterOfNone: His stats are middle of the road, and he gets no starting item to work with, unlike the others. [[spoiler:...Until you unlock the D6.]]
* MeaningfulName: The Biblical Isaac was going to be sacrificed to God by his father Abraham under orders from God himself. Sounds a lot like what's happening to Isaac... sort of.
[[/folder]]

[[folder:Magdalene]]
!!Magdalene
[[quoteright:148:https://static.tvtropes.org/pmwiki/pub/images/magdalene.png]]
->Debut: ''The Binding of Isaac''
Named after a friend of Mary, the mother of Jesus, she is distinguished from Isaac by her blonde hair and bow. Maggy represents the cleric class from traditional games and starts with the Yum Heart: an activated item that restores one heart upon use.
----
* BoringButPractical:
** Her gimmick is somewhat bland compared to the others, but having four red hearts to work with allows for Devil Room deals early on without severe consequences. Additionally, the Yum Heart restores a red heart every 4 rooms (without any items that accelerate charging), which keeps her healthy and can be a godsend during the later chapters.
** In ''Afterbirth+'', you can unlock a starting Speed Up pill for her through the challenges. Not flashy, but it does patch up her biggest weakness, and it takes up a slot in the pill pool that could otherwise be occupied by something less desirable.
* CombatMedic: Called "the cleric" in the art booklet.
* DeadPersonImpersonation: [[spoiler:The death of the real Maggy seems to be what caused Isaac's family to fall apart.]]
* InSeriesNickname: Usually referred to as Maggy.
* OneSteveLimit: Averted; she as the same first name as Mom.
* StoneWall: Maggy has low speed and bad tear damage, but has the highest starting health and the Yum Heart by default.
* TertiarySexualCharacteristics: Longish hair and a bow.
* UselessUsefulSpell: Yum Heart with certain playstyles can become this. If you need to use it (read: took red heart damage), your chance at getting powerful Devil Deal items got severely cut.
[[/folder]]

[[folder:Cain]]
!!Cain
[[quoteright:112:https://static.tvtropes.org/pmwiki/pub/images/cain15.png]]
->Debut: ''The Binding of Isaac''
Named after the biblical son of Eve and first murderer, he is distinguished from Isaac by an eyepatch. He represents the Thief class from traditional RolePlayingGames and starts the game with the Luck Foot: a passive item that improves random events in various ways. In ''Afterbirth'', donating 67 coins to the donation machine at the end of Greed Mode allows him to start with the Paper Clip, a trinket that allows him to open chests without using keys.
----
* BaldOfAwesome: Just like Isaac.
* BornLucky: Cain's starting item gives him increased luck in certain situations.[[note]]Pills will never have negative effects (in the original), RewardingVandalism is more likely to happen, the odds of winning the Skull game increases from one-third to one-half, and gold chests are more likely to give items (as opposed to pickups).[[/note]]
* EyepatchOfPower: He has an eyepatch, and also starts with higher attack than most other characters.
* FragileSpeedster: Starts with great speed and attack and an average rate of fire, but suffers from low range and health. Outright called "the thief" by the art booklet.
* GlassCannon: Starts with great attack and a good rate of fire, but lower health than usual.
* HeartIsAnAwesomePower: After the release of ''Rebirth'', Cain was widely considered the worst (non-joke) character with his sub-par stats and his newly nerfed items. His only saving grace was that when it came to money, there was no one who could reliably get and keep as much as him. Come ''Afterbirth'', Cain became widely considered the absolute best character for the new Greed Mode, which is all about money (his new general stat buffs certainly didn't hurt either).
* MasterOfUnlocking: In ''Afterbirth'', where you can unlock the Paper Clip trinket as a starting item for him, allowing him to unlock golden chests without using keys.
* NameOfCain: While not outright evil, Cain is somewhat shady-seeming — he wears an EyepatchOfPower and his abilities make him resemble a "rogue" class.
* {{Nerf}}: The mechanics of Lucky Foot changing in ''Rebirth'' indirectly hurt him '''REALLY''' bad. ''Afterbirth'' compensates a bit, as stated above.
* UnexpectedlyRealisticGameplay: Downplayed and it doesn't cause any real puzzles, but his eyepatch does factor into gameplay. For most characters, Technology 2 stacks the beam on top of their tears. Cain's the exception, his tears being shut off due to his eyepatch. Chemical Peel and Blood Clot are changed, too; while with other characters, every other tear will have increased damage due to one half of the face being scarred, with Cain, every tear has a 50% chance of dealing increased damage.
[[/folder]]

[[folder:Eve]]
!!Eve
[[quoteright:124:https://static.tvtropes.org/pmwiki/pub/images/eve.png]]
->Debut: ''The Binding of Isaac''
Named after the first woman and original sinner, Eve is distinguished from Isaac by long dark hair and eyeshadow. Representing the druid class from traditional games, she starts with [[CriticalStatusBuff The Whore of Babylon]], which [[TransformationOfThePossessed turns her into a demon]] at low health, and the [[AttackAnimal Dead Bird]], which fights for her when she is damaged. After donating 439 coins to the Greed Machine, she also starts with the Razor Blade, which lets her damage herself on demand.
----
* AdamAndOrEve: Named for the Biblical Eve.
* AttackAnimal: The Dead Bird.
* AwesomeButImpractical: In the normal game, her Razor Blade is this. It damages the player and gives an attack boost for the current room, which is fairly useless over multiple rooms and only good for getting the Whore of Babylon to activate on the first floor. In Greed Mode, however, it's a lot more useful since Angel/Devil Rooms are guaranteed by beating the final wave.
* CastFromHitPoints: The Dead Bird is activated by taking damage in a room and works as a faster level three Meat Boy for the room in which it activates. The Razor Blade removes a full heart when used, and increases damage for one room in return.
* CombatSadomasochist: Both of her starting items (and the items she can unlock) are CastFromHitPoints, and she is the only character who doesn't leave a puddle of urine upon entering a room with half a red heart; instead, she leaves blood. ''Afterbirth'' ups the ante if you donate enough coins in Greed Mode, by giving you the Razor Blade.
* CriticalStatusBuff: When she's down to half a heart, her Whore of Babylon powerup grants her greatly increased attack. ''Rebirth'' buffed this by allowing it to activate at one full heart.
* CursedWithAwesome: The "curse" that Eve starts the game with.
* DifficultButAwesome: Starts with terrible attack stats, but getting the most out of Eve's CriticalStatusBuff makes her a OneHitPointWonder with higher starting attack than most other characters.
* EmoTeen: Definitely evokes the stereotype, both in looks and in playstyle. You can even unlock the Razor Blade as a starting item for her, as if it weren't obvious enough.
* FourIsDeath: Eve is the fourth playable character, with a risky playing style that actually benefits from [[CursedWithAwesome being close to the brink of death]]. [[spoiler:In Ending 11, the character montage showed Eve being present at the game's fourth level, the Womb. And considering [[OffingTheOffspring how Mom is...]]]]
* FragileSpeedster: High speed, low health, low attack unless reduced to critical health.
* GlassCannon: Becomes one when hurt due to her CriticalStatusBuff.
* LooksLikeCesare: Has eyes encircled with black as well as black hair (though not scraggly).
* NoPeriodsPeriod: Averted via an EasterEgg. Every other character leaves a puddle of urine if they enter a room with half a heart left, but Eve leaves a bloodstain.[[note]]This was absent for most of ''Rebirth'', but returned in Booster Pack 5[[/note]]
* SecretArt: Eve is the only character that activates Whore of Babylon at one full heart remaining rather than half a heart. Additionally, it also changes her innate damage multiplier while active (Eve normally has a 25% damage penalty that is removed when Whore of Babylon activates), which it doesn't do for any other character.
* TertiarySexualCharacteristics: The Dead Bird in her hair looks like a bow.
* UselessUsefulSpell: A few items that regenerate half-red hearts passively are normally somewhat useful, but can be detrimental to Eve if they take her out of her CriticalStatusBuff and has soul/evil hearts protecting her red hearts.
[[/folder]]

[[folder:Judas]]
!!Judas
[[quoteright:112:https://static.tvtropes.org/pmwiki/pub/images/judas.png]]
->Debut: ''The Binding of Isaac''
Named after the disciple who betrayed Jesus, he has a [[NiceHat fez]] to distinguish himself from Isaac. He represents the mage class from [[RolePlayingGame RPGs]] and starts the game with the [[StatusBuff Book of Belial]], an activated item that increases attack power for one room. In the original game, he unlocks after beating the Womb for the first time. In ''Rebirth'', he unlocks after beating Chapter 5 for the first time.
----
* BaldOfAwesome: Just like Isaac.
* DealWithTheDevil: While holding the Book of Belial, the chances of a Devil Room appearing are increased. Unfortunately, Judas' starting 1 heart makes it impossible to make deals unless he gets more heart containers or soul hearts, or buys an item that grants him black hearts. Fortunately, passing up Devil deals means that subsequent Devil Rooms can be replaced by Angel Rooms, which give you free stuff.
* DifficultButAwesome: Starts off with the most consistent damage of all the playable characters (Eve and Samson's powers are conditional), but with only one starting heart and average speed for dodging, you don't have much leeway to screw up.
* GlassCannon: More so than Cain. Starts with an average rate of fire, range, speed, and high attack power, further bolstered by his [[StatusBuff Book of Belial]]. In exchange, he starts with only 1 heart.
* NiceHat: [[http://edmundm.com/post/85254517860/wasnt-judas-fez-because-of-phil-fish Edmund]] based Judas' ''VideoGame/{{Fez}}'' on Phil Fish, due to him [[TakeThat voting against Edmund and his comrades at the Independent Games Festival]]... although Edmund later stated that said explanation wasn't true, but he went along with it for a while because he found it funny.
* SecretCharacter: There's a form of Judas in ''Rebirth'' only attainable by dying with the Judas' Shadow item. For the rest of the run, you will play as a character known as Black Judas in-game, who has a 2.0 damage multiplier but starts only with two Black Hearts. Finishing a run as Black Judas counts as a Judas run for unlocks and achievements.
* SquishyWizard: The artbook refers to him as the "mage", fitting in the other RPG archetypes. It fits since Judas has high starting damage (especially with the Book of Belial active) but very low starting HP.
* StatusBuff: The Book of Belial increases his damage for a single room, which is especially handy for multi-wave rooms like challenge rooms, Greed mode, or the Boss Rush.
[[/folder]]

[[folder:???]]
!!???
[[quoteright:112:https://static.tvtropes.org/pmwiki/pub/images/bluebaby.png]]
->Debut: ''The Binding of Isaac''

Unlocked after defeating Mom's Heart/It Lives ten times, ??? is a shout-out to Edmund [=McMillen's=] Newgrounds account (specifically his "Dead Baby Dressup" game). Starts with [[JokeItem The]] [[ToiletHumor Poop]], which creates a pile of dung once per room. Whilst his official name is [[MyNameIsQuestionMarks ???]], his nickname is "Blue Baby", which is how he signs his death note on the GameOver screen (and how he's listed on the PSN Trophies list for ''Rebirth''). ??? starts with three soul hearts and is unable to use red hearts at all. Any red heart-granting items will be converted into soul hearts.\\
\\
Despite being a JokeCharacter gameplay-wise, he is possibly one of the most plot-relevant characters in the game. His reveal indicates that the vignette of Isaac suffocating in the chest is canon, and not only that, but he somehow died of asphyxiation whilst there. At this point, it is implied that Isaac has been DeadAllAlong and Endings 11 and 12[[note]]12 and 13 in ''Rebirth''[[/note]] seem to indicate that Isaac actually locked himself in the chest after being DrivenToSuicide.
----
* AmazingTechnicolorPopulation: [[JustifiedTrope Justified]], since he's dead and cyanotic.
* JackOfAllStats: No outstanding stats or notable starting item, with the exception of his "-1 HP", meaning that he depends on soul hearts just to live. However, he is actually slightly faster and stronger than Isaac.
* JokeCharacter: Blue Baby is incapable of gaining red heart containers; any situation that would give him red hearts instead converts them to soul hearts. Also, soul hearts remain much rarer drops than regular hearts, making getting hit even less feasible. At least he can still gain black hearts...
** LethalJokeCharacter: Since his health can only be composed entirely of soul and black hearts, he can exploit certain health-based mechanics (such as the Whore of Babylon, which is permanent if picked up), leading to quite a few potential and powerful combos. He also has permanent access to Devil and Angel Rooms, since he's not taking red heart damage.
* JokeItem: The Poop; it only creates a mound of poop like those you usually see. However...
** LethalJokeItem: ...you'd be surprised how situationally useful The Poop can be. A pile of poop spawned can be used to create a temporary cover, and can be bombed like a rock to cross single-tile-wide gaps. It is affected by the Petrified Poop trinket (which it can also create), meaning you can get a coin every room or two if you have it. In ''Afterbirth'', using the Poop deflects incoming projectiles a la buffed Butter Bean.
* MechanicallyUnusualClass: Tamer than later examples, but his restriction on hearts makes quite a few items work very differently for him as noted. Most health ups are bad or useless, but anything that gives soul hearts is exponentially more powerful.
* MyNameIsQuestionMarks: A unique example in that it's never revealed what the question marks are obscuring (unless you go with the theory that he's just a postmortem Isaac).
* NoDeadBodyPoops: [[RealityEnsues Oh yes they do.]] [[AvertedTrope Which is the whole point]] of his JokeItem.
* NotQuiteDead: Well, his body ''is'' dead, but he's moving around and acts normally despite being a corpse.
* SecretCharacter: While he's on the menu from the very start, new players probably won't assume that "???" is his actual name. His secrecy is lessened by him being first Secret Character players are likely to unlock, and the only one unlocked by playing the game normally.
* ToiletHumor: You can't get much closer to this than being able to poop on command.
* UndeadChild: He's the corpse of a child that's somehow still animate.
* TheUnpronouncable: He's usually just referred to as "Blue Baby", even on his last will, since "???" isn't exactly easy to pronounce.
* WingdingEyes: Crossed-out eyes.
[[/folder]]

[[folder:Samson]]
!!Samson
[[quoteright:120:https://static.tvtropes.org/pmwiki/pub/images/samson.png]]
->Debut: ''Wrath of the Lamb''
Introduced in ''[[ExpansionPack Wrath of the Lamb]]'' and named after the biblical strongman, he has long, brown hair and BigOlEyebrows. He also starts with a red headband called [[StatusBuff Bloody Lust]]. This is fitting with the fact that he represents the Berserker class. An extremely important part of this character is how he was substantially changed. In the original, Samson started with one heart container and gained a damage boost for every enemy he kills in a room. In ''Rebirth'', he starts with three heart containers and gains a damage boost every time he takes damage, which lasts for an entire floor.
----
* TheBerserker: Bloody Lust can actually support AttackAttackAttack to an extent, with the damage he takes actively improving how fast he can end the fight and letting him keep that improved damage for the whole floor.
* BloodKnight: His trademark power-up is called Bloody Lust, after all!
* ConservationOfNinjutsu: {{Invoked|Trope}} by his special hair-band. The more enemies you face in a room, the more powerful you'll get! But single-target rooms won't trigger any attack-boost. This is changed in ''Rebirth'', although re-added in ''Afterbirth'' as an unlockable item called [[{{Spoonerism}} Lusty Blood]].
* CriticalStatusBuff: In ''Rebirth'', Bloody Lust makes Samson deal more damage as he ''takes'' damage, with him reaching near maximum damage for having taken several hits in a row. In this case, he literally TurnsRed to reflect Bloody Lust activating.
* DifficultButAwesome:
** In ''Wrath of the Lamb'', Bloody Lust makes Samson powerful... if you manage to survive the hordes of enemies that give him his strength. Only having a single heart (later a soul heart as well) makes that easier said than done.
** In ''Rebirth'', this mechanic is changed, although he's still a challenging character. Bloody Lust now only triggers when taking damage and the bonus is lost at the end of the floor. That means he has mediocre damage if you don't take hits, and can't manipulate it the same way Eve can.
* GatheringSteam: In the original, he gains damage as he kills enemies, but loses it after he leaves the room.
* GlassCannon: With just 1 starting heart container, he's as fragile as (and under some circumstances, even more than) Judas. However, his special gear makes him extremely effective against large groups of enemies and/or {{mook maker}}s. This is changed in ''Rebirth'', which gives him much more starting health; however, in order to max out his damage output, he has to deliberately take a lot of damage.
* MartialArtsHeadband: It's the source of his Blood Lust passive ability.
* PowerupLetdown: He's probably the most difficult character to unlock in the original (with [[spoiler:???]] possibly being more tedious than difficult), as it requires you to pass on 2 free items on a regular run... and its capacity is dubious, to say the least. After months of complaints, Edmund promised a buff to Samson. The buff was starting with a soul heart on top of his single regular heart... which didn't change all that much. He became much more useful in ''Rebirth'', as he now starts with three regular hearts and his buffs from killing enemies and taking damage remain until you leave the floor. On the other hand, now you have to clear two floors in a single run without taking any damage to unlock him, which is arguably even more difficult.
* TookALevelInBadass: In ''Rebirth'', Samson starts with a much more forgiving 3 hearts and gets to keep his buffs until he leaves the floor. This is a major improvement from his previous incarnation.
* UnstoppableRage: What Bloody Lust represents as of ''Rebirth''.
[[/folder]]

[[folder:Lazarus]]
!!Lazarus
[[quoteright:112:https://static.tvtropes.org/pmwiki/pub/images/lazarus.png]]
->Debut: ''Rebirth''
Named after the one that was brought back from the dead. Unlocked in ''Rebirth'' by having four or more soul hearts at once. He starts with average stats, but has Lazarus' Rags, which allows him to return as Lazarus Risen after dying and giving him [[OverdrawnAtTheBloodBank Anemic]]. His gameplay is unique in that to gain a fairly powerful item and stat boosts, the game encourages you to kill yourself.
----
* BackFromTheDead: Starts play with one extra life.
* BornUnlucky: He starts with negative luck, although this is cleared upon resurrecting.
* BloodyMurder: After he uses his extra life, he gets the Anemic item, which lets him leave a damaging trail of blood for the duration of the room upon taking damage. Beating the Backasswards challenge makes this trail permanent instead.
* CameBackStrong: Lazarus Risen is statistically better than normal Lazarus in every way aside from health, in addition to gaining Anemic (or, if unlocked, leaving a permanent blood trail). Many players choose to kill themselves as soon as they have a health up available, circumventing the lower health and coasting off the increased stats.
* CrutchCharacter: One of the first characters available to unlock, he has a higher tolerance for damage than Isaac, with the only apparent downside being his negative luck. After unlocking [[spoiler:the D6]], however, his advantage seems rather insignificant. Without using his extra life very tactically, he ultimately plays like a less lucky Cain or a less powerful Judas... [[TookALevelInBadass until you complete Challenge 31]] in ''Afterbirth+''.
* MasterOfNone: Apart from his resurrection ability, he essentially plays like [[MasterOfNone Isaac]] [[spoiler:without a D6]].
* MeaningfulName: [[http://en.wikipedia.org/wiki/Lazarus_of_Bethany Who else but Lazarus]] would start with the ability to rise from the dead?
* NotQuiteDead: His gimmick is being able to resurrect instantly, rather than outside the room he died in (forcing him to restart it).
* PowerupLetdown: His extra life only resurrects you with exactly one heart container, and only gives you a blood trail for the current room if you get hit once. On the other hand, it does resurrect you on the spot (unlike the other extra lives that return you to the previous room), possibly allowing you to finish off whatever killed him. Lazarus also receives a considerable boost in Luck, Range, Damage, and Speed, but still, that one heart container makes it a tricky run.
* TookALevelInBadass: Completing Challenge 31 in ''Afterbith+'' allows him to use Anemic right from the start without losing his extra life first. Additionally, it is activated permanently if Lazarus dies and is resurrected (or another character resurrects as him), with no need to take damage.
* TouchedByVorlons: Downplayed with his Lazarus' Rags item. Before dying, his stats are nothing to write home about. [[BackFromTheDead After dying and reviving]], his stats receive a buff and he now leaves a trail of blood whenever he takes damage (or permanent if Challenge 31 in ''Afterbirth+'' is cleared).
[[/folder]]

[[folder:Azazel]]
!!Azazel
[[quoteright:152:https://static.tvtropes.org/pmwiki/pub/images/azazel1.png]]
->Debut: ''Rebirth''
A demonic-looking character whose name is associated with evil. Unlocked in ''Rebirth'' by making three deals with the devil in one run. Starts with the ability to fly and a short ranged version of [[HighPressureBlood Brimstone]].
----
* ActionBomb: He starts with only black hearts, which trigger the [[SmartBomb Death]] effect when depleted.
%%* [[BigRedDevil Big Black Devil]]
* CloseRangeCombatant: Until [[spoiler:The Forgotten]], he was the closest thing that ''Rebirth'' had to one, since his starting weaponry forces him to get relatively close to enemies. He compensates by possessing above-average speed and flight.
* CrutchCharacter: Despite his low range, Azazel's flight and high damage make him by far the easiest character to play as. However, he plays entirely differently from every other character, meaning that playing with him doesn't build the skills you need to be good with the rest of the characters. In addition, many items have no effect on his short-range Brimstone, so he's locked out of a lot of neat synergies. Finally, the final bosses indulge in BulletHell, which makes them much tougher to beat with Azazel since you constantly risk getting shot in the face.
* DarkIsNotEvil: He's a demon and starts with Black/Evil Hearts, but he's still a playable character just trying to escape the basement dungeon.
* DiscOneNuke: His flight and Brimstone are a major advantage in the early game, and flight remains an important bonus throughout. However, his limited range will really begin to catch up to him when it comes time to face the endgame bosses.
* DungeonBypass: Possessing flight lets him ignore spikes, rocks, and other terrains right from the start. Rather useful.
* FragileSpeedster: Fast, possesses flight and has high starting damage, but at the cost of poor range that cannot be increased and having to charge Brimstone for attacks. His black hearts damage everything if one gets depleted and he can eventually gain red heart containers through Health Up items, but he is overall much frailer than characters who can pick up red hearts from the get-go.
* FrickinLaserBeams: His starting attack is a limited-range Brimstone.
* GlassCannon: High damage, but starts with no red hearts.
* GoodWingsEvilWings: Subverted. Azazel has demon wings but is good ([[spoiler:[[ThroughTheEyesOfMadness or at least on Isaac's side]]]]) and also on the same side as Apollyon, who has angel wings.
* HitAndRunTactics: Unlike others who depend on kiting with tears, Azazel often has to fly in, blast several enemies with brimstone, then get out of there before the rest retaliate. He can also strafe multiple enemies for the duration of his Brimstone, but again, he has to be closer than normal for tear-strafing.
* HornedHumanoid: One of his horns is broken.
* TheLastOfTheseIsNotLikeTheOthers: At the time of his release, Azazel was by far the most different from the other playable characters, since he starts with miniature brimstone instead of tears, has evil hearts (but can gain red ones, unlike [[spoiler:???]]), and has flight (which only [[spoiler:The Lost]] shares). The result is a rather different playstyle, including item selection, since his smaller brimstone makes many items useless/redundant, but makes others extremely powerful.
* NecessaryDrawback: Though Azazel can increase his Brimstone's range with upgrades, the benefit is almost entirely negligible unless you pick up several of them, which is unlikely without the use of items and consumables which can re-roll items. In addition, his short range negates any homing effects.
* RedEyesTakeWarning: He has these to add to his demonic appearance and he's one of the most powerful characters in the game.
* RequiredSecondaryPowers: At the time, a melee character would've been an interesting addition to the roster, but being forced to rely on an actual melee attack would make multiple rooms UnwinnableByDesign. Azazel being equipped with the piercing brimstone and flight fixes both of these problems. A true melee character eventually came along in the form of [[spoiler:The Forgotten]], which has its own set of RequiredSecondaryPowers.
* WingedHumanoid: Starts with flight.
[[/folder]]

[[folder:Eden]]
!!Eden
[[quoteright:112:https://static.tvtropes.org/pmwiki/pub/images/eden.png]]
->Debut: ''Rebirth''
Named after the biblical garden, Eden's stats and starting items are randomly generated every time you play as them. Their gender is undefined, and to play as them requires the use of one "Eden token", earned by beating Mom's Heart/It Lives! or Ultra Greed. Unlocks in ''Rebirth'' after beating the Womb for the first time.
----
* AnimeHair: The hairstyle is random, and many options look like this. The colour is always [[MysticalWhiteHair white]].
* ConfusionFu: Always starts with a random set of items and stats.
* LuckBasedMission: The stats and item(s) you start off with are randomized each time, making it equally possible to have a strong early advantage or a really weak one. Most character power level discussions simply leave Eden out because of how much inconistent Eden runs are.
* MonochromaticEyes: In the ending that unlocks the character and on the character select screen. You can give any character these eyes by picking up Eden's Blessing.
* MysticalWhiteHair: The mystical part coming from their random stats and starting items.
* NecessaryDrawback: As Eden's random stats can potentially give you either very good or very bad combinations, each Eden run consumes an Eden token, and you only earn one each time Mom's Heart/[[spoiler:It Lives]]/Ultra Greed is beaten. This is to discourage reset spamming for a good[=/=]game-breaking item combination.
* OtherworldlyAndSexuallyAmbiguous: WordOfGod is that Eden lacks gender. [[http://bindingofisaac.com/post/86958618769/spoiler-alert-you-unlocked-eden As described]] [[WordOfGod by]] Creator/EdmundMcMillen:
--> Eden isnt a man, nor are they a woman.. they just are. %%[sic], directly copied from http://bindingofisaac.com/post/86958618769/spoiler-alert-you-unlocked-eden — I don't know if it's policy to correct such quotations or not.
[[/folder]]

[[folder:The Lost]]
!!The Lost
[[quoteright:112:https://static.tvtropes.org/pmwiki/pub/images/thelost.png]]
->Debut: ''Rebirth''
A ghost character, and one of the only characters not based off of any sort of religious context[[note]]unless it refers to the "souls lost in Limbo"[[/note]], next to ???. It is the secret character of ''Rebirth'' and had a '''very''' complicated unlock process… until ''Afterbirth'' came along.\\
\\
In ''Rebirth'', The Lost starts with flight, but [[OneHitPointWonder dies if he takes any damage]], with the inability to ever pick up health. ''Afterbirth'' significantly buffed The Lost, granting him spectral tears and The D4 by default, as well as letting him unlock Holy Mantle, giving him a shield that blocks one hit per room.
----
* BalanceBuff: ''Afterbirth'' gave him the potential to start with the D4 and the Holy Mantle. Plus, he gained spectral tears, letting him cheese difficult rooms by hanging out over a rock and shooting enemies from safety.
* ChekhovsGunman: Actually, it appears several times prior to being unlockable, albeit so briefly that few players would actually notice. Specifically, it is the ghost that departs from Isaac every time he dies.
* DifficultButAwesome: With zero health and only one free hit per room with the Holy Mantle, you need to be good at dodging. If you can manage, however, and get lucky with free Devil Room deals, Black Market deals, and cursed room items, you can end up with a flying GlassCannon powerhouse.
* GlassCannon: And how! It has ''zero health'' and can't gain any type of hearts, period. The only upside to this is that it takes Devil Room and Black Market upgrades for free, possibly resulting in a OneHitPointWonder powerhouse early on.
* GuideDangIt:
** Unlocking it is a bit... convoluted. First, you need to let yourself get killed by a Mulliboom in the basement as Isaac. Next, you need to blow yourself up with one of your own bombs as Maggie in the caves, then let yourself get killed by Mom's foot as Judas. Finally, you need to let yourself be stomped to death by Satan's hoof as Azazel. And you need to do all of this ''in a row'', without winning or dying in any other way. Mess up once and you have to start all over again. Not very easy, to say the least, although the at the very least you get (cryptic) hints as to the next step once you've completed one, and you can use seeds to make it easier, in contrast to almost every other unlock. The "guide" was at least hidden in-game, though it would have been hard for one person to piece together. Dying in a sacrifice room while holding the Missing Poster trinket shows a puzzle piece as a cause of death. Putting the puzzle pieces together show the four game-over screens required to unlock The Lost.
** ''Afterbirth'' ''vastly'' simplified the unlock process; you just need to die in a Sacrifice Room while holding the Missing Poster. Of course, nowhere in the game does it tell you this, and the fact that the former method is much better-known doesn't help.
* JokeCharacter: Starts with the ability to fly and shoot spectral tears (which lets its attacks pass through objects)... with the downside of having ''absolutely no HP'', meaning it will die after a single direct hit.
* LethalJokeCharacter:
** Its lack of HP means that it can take Devil items (some of the most powerful items in the game) for no cost at all; normally, it would cost one or two heart containers for one of those items. This can lead to ''very'' powerful combos, turning it from a joke character into a feasible GlassCannon if you get multiple deals with the Devil in a single run.
** In ''Afterbirth'', this is cranked up hugely due to the Holy Mantle being unlockable as a default item. This means it can take an extra hit per room (so you both don't have to be absolutely perfect) that he can heal back each time you enter a room. It also has access to curse rooms at no cost.
* LethalJokeItem: A handful of terrible items become better in The Lost's hands, such as Glass Cannon not having a downside since you don't actually have any health to reduce.
* OneHitPointWonder: Dies in one hit from anything. Earlier versions had him die from ''continuing a run.'' In ''Afterbirth'', however, it is possible to earn the Holy Mantle shield as a starting item for him.
* OurGhostsAreDifferent: This one gets blown away by a stiff breeze.
* PowerUpLetdown: Some thought that Samson and ??? weren't worth the effort it took to unlock them, but The Lost is quite possibly even ''worse'' in this regard, especially since unlocking it involves a dose of GuideDangIt too. ''Afterbirth'' mitigates this by having The Lost start with the D4 (which allows it to reroll any items it is carrying) and spectral tears, as well as the Holy Mantle once you donate enough coins to the Greed Machine. Most notably, the powerful items you ''unlock'' by beating the game with are why people get him. As soon as that's over with, many players will choose to forget he even exists.
* UselessUsefulSpell: Once you unlock the Holy Mantle for the Lost, the D4 becomes this, simply because the ability to actually take a hit per room outweighs just about anything it can potentially be rerolled into. A large portion of the items in the game also fall into this category, namely any item that gives only health and anything that activates on taking damage.
* WalkingSpoiler: Naturally, being the secret character of ''Rebirth''.
* WhamShot: ''Afterbirth'' adds a new, interesting loading screen. That voice that told Isaac's Mom that he was evil? It was the Lost, speaking from the attic.
[[/folder]]

[[folder:Lilith]]
!!Lilith
[[quoteright:128:https://static.tvtropes.org/pmwiki/pub/images/lilith.png]]
->Debut: ''Afterbirth''
Named after Adam's first wife who defected from Heaven with Samael. She's also known as "The Mother of Demons." Unlocked in ''Afterbirth'' after clearing Greed Mode with Azazel. Starts out blindfolded, meaning she is unable to shoot tears, but also starts with the Incubus familiar whose tears have the same properties as hers, the Box of Friends active item which duplicates her familiars for one room, and the Cambion Conception passive item which permanently grants a new familiar upon taking a certain amount of damage.
----
* AwesomeButImpractical: Some of the Cambion Conception minions are extremely good, like Brimstone Baby or Dark Bum (!!), especially when doubled with Box of Friends. You'll need to take at least 15 hits ''per minion'' though, which is easier said than done with Lilith's starting health.
* CuteMonsterGirl: Appart from her bloody, bandaged eyes, she's a demon girl who is very human-looking.
* EyeScream: Implied by the bloodstains on her blindfold.
* GlassCannon: Box of Friends effectively doubles her damage output for a room, allowing her to deal significant amounts of damage, but with only one red heart, she struggles at taking hits.
* LethalJokeCharacter: While incapable of shooting tears herself, she starts with the item 'Box of Friends', which adds a copy of any familiars she has for a single room and takes four rooms to recharge. This makes her the best character by far in Greed Mode, as the battles on each floor take place in a single room, and she recharges the item every four waves of enemies. At a minimum, you can quadruple your friends by the end of the floor.
* HornedHumanoid: Has demon horns.
* MagikarpPower: If you can pick up more familiars or find a way to spawn at least one more with Cambion Conception without dying, Box of Friends' effectiveness begins to multiply. Gaining boosts to spacebar charge rate increases how often she can double her army of minions, and BFFS just makes everything stronger.
* MechanicallyUnusualClass:
** Lilith has a blindfold over her eyes, similar to challenge runs where you can't shoot any tears, or other tear-replacing attacks like Mom's Knife or Brimstone. She compensates for this by starting out with the Incubus, a powerful familiar that copies (for the most part) the player's tear stats.
** Lilith's Incubus is part of being Lilith. It will not reroll even with a full run re-roll; you can pick up a second Incubus normally; and if you somehow change from Lilith to another character, you lose the Incubus.
* {{Nerf}}: Her active item, Box of Friends, was nerfed in a patch about a week after ''Afterbirth's'' release, making it a 4-room charge instead of 2. This brought Lilith down from "Amazing character that can cut through the game with ease with her army of minions" to "Good, but not great."
* TheMinionMaster: Starts with a familiar as her only way to deal damage. Her Box of Friends active item creates a copy of each familiar she possesses when used (copied familiars don't count, so only the originals are duplicated), and her Cambion Conception gives her another (permanent) familiar if she is damaged a certain number of times (which, as stated under the GlassCannon entry above, can be tricky due to her low starting health).
* MookMaker: Playable variant. Lilith starts with Cambion Conception, which permanently spawns a new demonic buddy after taking enough damage by giving birth to it, if the progressively more and more pregnant appearance is anything to go by.
[[/folder]]

[[folder:Keeper]]
!!Keeper
[[quoteright:112:https://static.tvtropes.org/pmwiki/pub/images/keeper2.png]]
->Debut: ''Afterbirth''
A character unlocked by the efforts of the community in the ''Afterbirth'' [[AlternateRealityGame ARG]], Keeper is the corpse of Isaac that killed himself by hanging. He becomes playable by donating 1000 coins to the Greed Machine. His name refers both to the shopkeepers he resembles and to Cain's words in the book of Genesis, "Am I my brother's Keeper?" He starts with a triple shot, is healed by pennies, and cannot pick up hearts. Hearts he is given become Blue Flies.
----
* BackFromTheDead: Like ???, he is an undead Isaac. In this case, one who paid for his greed and became one of the greyed corpses you see running the shops.
* ChekhovsGunman: He appears in Ending 18 as the corpse of Isaac that shrivels up to a shopkeeper.
* DoubleUnlock: Although the ARG "unlocked" him by adding him to the game, he's only playable after donating one thousand coins to the Greed Machine.
* TheGambler: He has a lot of coin-themed unlocks, which are frequently chance related. Once Isaac is defeated he also starts with the Wooden Nickle, which gives him a 50/50 at generating one coin per room.
* GoodCounterpart: He's a Keeper monster who's on Isaac's side, and his combat style is identical to that of that of Greed.
* GlassCannon: By default, he has above-average damage and a triple shot. Just giving him some fire rate boosters makes him dish out pretty decent damage. However, he is usually never more than two hits away from death, with special items like Holy Mantle (and its weaker counterpart the Wooden Cross and Safety Blanket) and Greed's Gullet being the only ways to extend that.
* GuideDangIt: Not necessarily his unlock, but to ''unlock'' his unlock. [[AlternateRealityGame A long series of cryptic hints led to a treasure hunt in Santa Cruz, CA, culminating in the discovery of a small buried Keeper doll.]] This led to the patch being released on Steam that added Keeper to the game.
* JokeCharacter: Probably the biggest of the three.
** Instead of hearts, Keeper has two coin slots (and can only have a maximum of two); any kind of damage takes a health coin (which still counts as red heart damage for the purposes of Devil/Angel Room generation), but taking another coin on the floor heals it back '''without''' increasing your coin count. This means that Curse Rooms (without Holy Mantle) and two-heart Devil deals will straight-up kill him, while one-heart Devil deals leave him as a OneHitPointWonder. All health-increasing items are worthless unless you've lost one coin slot already. He also can't take soul or black hearts, as they get converted into flies.
** Keeper has an innate triple shot, but his fire rate isn't programmed as the normal Inner Eye item would, so it's effectively even lower than that of The Inner Eye.
** Keeper's starting items aren't available [[MagikarpPower until you unlock them]], and they're mundane at best. The Store Key trinket only opens access to shops, whereas the Wooden Nickel has a chance to fail, as seen in LethalJokeItem below, and he only starts with a bomb (and a penny when you unlock it... by beating ''[[DudeWheresMyReward Hush]]'').
* LethalJokeCharacter: In a few ways, though still less so than its counterparts.
** Since Keeper's triple shot's fire rate isn't programmed as the normal Inner Eye item would, by picking up enough Tear stat boosters (and by enough, we mean A LOT), it's still possible to end up with the regular maximum fire rate possible.
** It's possible to extend his life with a few items. A Swallowed Penny or the Piggy Bank drop coins in battle if he gets hit, which will restore his health if picked up. Meanwhile, Greed's Gullet is the only item capable of extending his health above the maximum by picking up coins and ''never spending them''.
** In Greed Mode, Keeper effectively gets hearts every wave that can be picked up mid-combat provided the player is fast enough. The only downside is that doing so decreases the money available to buy pickups and items. This extends to Ultra Greed's battle; since his attacks make you drop coins on contact, you just keep getting health back, and since Ultra Greedier's attacks generate coins during the fight, you'll never run out short of gross incompetence.
* LethalJokeItem: {{Zig|Zagging Trope}}-zagged. By unlocking the ability to start with the Wooden Nickel, it's possible to generate a coin to heal him back. Problem is, ''it has a 50/50 chance of working''.
* MechanicallyUnusualClass: Has the most unconventional playstyle of the {{Joke Character}}s. He has only two hit points, but those are coins instead of hearts. Any heart pickups that appear are replaced by friendly flies.
* MagikarpPower: [[DownplayedTrope Downplayed]]. He's a difficult character to play as, but by defeating certain bosses as Keeper, you can get some mundanely useful starting items for him (and a single dumb penny), making him... still pretty difficult to play, but at least a little better. He's much more useful in Greed Mode, as he can rapidly build up coins and heal back any damage taken. The Wooden Nickel item is also quite nice, if unreliable.
* SecretCharacter: Doubly so. He isn't listed on the character screen until he's unlocked. More than that, he wasn't even added to the game data until a real-life ARG was completed, preventing the datamining debacle that uncovered The Lost.
* TheTheTitleConfusion: Unlike fellow secret characters The Lost and The Forgotten, Keeper is just Keeper. That doesn't stop most of the community from referring to him as The Keeper anyway.
* UndeadChild: Distinct from ??? in that his cause of death is from hanging, not suffocation.
* WalkingSpoiler: Like the Lost, he is a heavily hidden character. The developers even took care for him to not be discovered by hackers before his ARG had been concluded.
[[/folder]]

[[folder:Apollyon]]
!!Apollyon
[[quoteright:112:https://static.tvtropes.org/pmwiki/pub/images/apollyon_5.png]]
->Debut: ''Afterbirth†''
A mysterious new character who debuted in ''Afterbirth†'' who is unlocked by killing Mega Satan for the first time. He starts with the Void item, which destroys and copies the effects of activated items while turning passive ones into random stat boosts. Apollyon is the Greek name of (and he therefore represents) Abaddon, the angel of destruction and the abyss in Revelations, the last book of the Bible.
----
* TheAssimilator: Void destroys passive items and turns them into stat boosts, and gains the effects of any active items it destroys. The latter can stack indefinitely, so Void can become a pretty ludicrous item by the end of the game.
* BlackEyesOfEvil: His eyes are completely black. On the loading screen between floors, they look like hollow holes.
* DifficultButAwesome: Using the Void item to its fullest potential (and therefore [[MagikarpPower mitigating Apollyon's pitiful stats]]) requires to player to understand how pretty much every item in the game works and whether or not they're worth picking up vs. Voiding vs. leaving it behind altogether.
* FallenAngel: Mentioned to be one of his character traits in the blog post. In addition, his name is Greek for the Hebrew word Abaddon, which means he could represent the angel of destruction and has a relation to [[spoiler:Sheol]].
* GoodWingsEvilWings: He has a pair of feathery wings. He is one of the playable characters, so he's good.
* HornedHumanoid: He has two small black horns.
* MagikarpPower: Starts with 2 hearts and average~low stats, and his starting item Void does nothing initially. However, Void can convert unwanted passive items into random stat boosts and absorb the effects of activated items permanently. This allows you to turn useless items into damage or other benefits, and Void's ability to stack effects allows for insane combos that can shatter the game if you luck out and find the right items.
* MeaningfulName: His name is the Greek word for "''destroyer''". Sure enough, his main ability is to destroy items to gain their abilities or stat bonuses.
* MundaneUtility: Void allows Apollyon to turn cruddy or detrimental passive items into more useful stat boosts, though he's out of luck if he finds bad or detrimental active items.
* {{Nerf}}: Void initially kept any single-use items it sucked up, allowing them to be used again and again. This caused some truly gamebreaking stuff, like having [[NukeEm Mama Mega]] every floor. It was quickly changed to use the item once and never again, to very few people's complaint.
* PowerOfTheVoid: A successful Apollyon run depends in big part on judicious use of his Void starting item, which can turn into an all-powerful item and/or give Apollyon massive stat increases by the end of the run.
* TheSwarm: Not in-game, but most of Apollyon's unlocks are locust trinkets of some kind, as a reference to the biblical Apollyon's status as the king of an army of locusts.
* WingsDoNothing: Unlike Azazel, he doesn't use his wings for flight. They're just decoration.

[[/folder]]

[[folder:The Forgotten]]
!!The Forgotten and the Soul
[[quoteright:111:https://static.tvtropes.org/pmwiki/pub/images/forgotten.png]]
[[caption-width-right:111:The Forgotten]]
[[quoteright:100:https://static.tvtropes.org/pmwiki/pub/images/soul_0.png]]
[[caption-width-right:100:The Soul]]
->Debut: ''Afterbirth†''

The Forgotten is a skeletal character added in the fifth Booster Pack for ''Afterbirth†''. He has a melee attack and uses a special type of "bone hearts," and can switch to a ghost called the Soul, which plays similarly to the Lost and is chained to the Forgotten. All red hearts become bone hearts and are given to The Forgotten. All soul and black hearts go to The Soul. He is unlocked by assembling a special shovel and using it on a room late in the game.
----
* BallisticBone: The Forgotten can throw his bone like a boomerang, the distance determined by how long you charge it. It's much weaker if used as such, though, making the Soul preferable for ranged attacks.
* BarredFromTheAfterlife: Rather than moving on after death, the Soul is forever bound to the Forgotten. This is implied to be Isaac's final fate after committing suicide in the Chest.
* CantLiveWithoutYou: Dying as the Forgotten or the Soul is GameOver, regardless of the health of the other party. However, it is possible to kill the Soul through a Devil Deal and survive if you swap back to the Forgotten during the ItemGet animation; if you do this, the Soul will be disabled until you collect a Soul/Black Heart to restore it. Using the Converter to drain the Soul also won't kill you, merely force you back to the Forgotten once you've done it.
* CloseRangeCombatant: The Forgotten's bone club attack is fairly powerful, but requires him to get up close to use it. It can be thrown, but the damage is weak enough that it's easier to just use The Soul.
* DemBones: Well, he ''is'' a skeleton. The special bone hearts he uses (which become available as drops for all characters after he's unlocked) take three hits to deplete and can be refilled with red hearts, but are lost forever if they're destroyed.
* DifficultButAwesome: He plays ''nothing'' like any other character in the game, and you have to master being able to switch between the skeleton and its Soul when the situation best calls for it, which isn't easy considering that both the skeleton and the soul use different forms of health, and because of how they work, you can never have more than six bone hearts or six soul hearts. However, his melee attack is very powerful, and while the Soul is active, you can use the inactive skeleton to shield yourself from bullets without taking damage. The Soul also has flight and spectral tears, enabling him to fly over obstacles, pick up items, and fire through rocks just like the Lost, but without being a OneHitPointWonder. Additionally, the bone hearts are not counted as red health unless you completely break a bone heart, so you won't lose a chance at a devil deal just from taking damage as long as you can heal up. However, Devil Deals can only be taken by the Soul, so you have to have enough Soul/Black Hearts to survive it.
* GameBreakingInjury: Any heart container that he would normally acquire gets replaced by special Bone Hearts. Bone Hearts deplete within three hits instead of two: two for the heart, one for the bone covering. As long as the bone part remains, a normal red heart can refill it. However, if a Bone Heart is completely destroyed, it's gone for good until you collect another item that grants extra health or find a special Bone Heart pickup.
* GhostlyGape: The Soul has blank, black eyes [[ReflectionlessUselessEyes with no reflections]] and an open mouth.
* GuideDangIt: His unlock method is pretty convoluted. First, you need to kill the Basement I boss '''within one minute'''. If you manage it, you'll hear Mom calling for Isaac and loud footsteps. Return to the starting room and plant a bomb, then the first half of Mom's shovel will fall from above. This shovel will make Mom constantly try to stomp you through the entire time you hold it, and its active effect only ''stops'' this for one room or one Boss Rush wave. Oh, and it vanishes if swapped out for another active item. Then, beat the Boss Rush while holding the Shovel part to get the second part of Mom's Shovel, while handling the above stomping. Once the Shovel is complete, get to the Dark Room and find a room with a small mound of earth on it. Dig that mound with the Shovel and you'll unlock the Forgotten.
* HitAndRunTactics: Like Azazel, sometimes as the Forgotten you'll need to run in, take a swing or two with your bone club, then either run away or dodge before they retaliate before swinging at them again.
* ImmuneToBullets: While you're controlling the Soul, the Forgotten becomes an immobile, invincible skeleton. He can be used as a bullet shield in this state, and even attracts bullets to himself in a very short radius.
* TheLastOfTheseIsNotLikeTheOthers: To start with, he's a skeleton. He's also the only character who has a proper melee attack. On top of that, he's two characters in one and you can switch between the two on the fly.
* LethalJokeItem: Size up items not only increase the Forgotten's size, they increase the size of his melee weapon, giving him greater reach. If you manage to stack enough of them, you don't even need to aim. Conversely, size down items should be avoided, as they will reduce his range for the same reason. Thankfully, there is a hard minimum for the melee attack, so you can't render it completely useless.
* MechanicallyUnusualClass: The Forgotten is a double-character, with one side having a melee attack, and the other sharing mechanics of the Lost (flight and spectral tears) and ??? (can only collect soul hearts). Additionally, the Forgotten's melee attack interacts very differently with tear-changing powerups compared to other characters; for example, getting Mom's Knife sticks the knife on the end of his bone, increasing damage and the range of the swing.
* MundaneUtility: The Forgotten's melee attack can be used to open spiked chests without taking damage. Furthermore, hitting anything with the melee attack counts as touching it for the purposes of collection, which can be used to grab collectibles (but not items) from behind rocks or over short pits. This is normally redundant with the Soul's flight, but can come in handy if the Soul is disabled.
* NecessaryDrawback:
** Because the Soul possesses every advantage of the Lost except with the ability to gain health, he's chained to the Forgotten at all times, limiting your movement radius to a half-dozen tiles or so. This prevents you from fully exploiting his flight to avoid enemies, though it's more than enough to collect anything in a given room most of the time.
** Since the character uses dual health bars, the Forgotten and the Soul can only have 6 hearts total each. This is lessened by bone hearts being tougher to lose than normal hearts, but it's further exacerbated by them being rare and permanently destroyable. Also, you can't use soul hearts to protect your bone hearts, since they go straight to the Soul.
* RequiredSecondaryPowers: As the true melee character, The Forgotten has a few attributes to prevent certain rooms from being unbeatable, most notably the ability to either throw his bone club or switch to The Soul to deal with enemies across gaps or under spikes. The ranged abilities are also necessary to deal with self-destructing enemies without losing hearts.
* TagTeam: Their whole gameplay is based on the ability to switch between the Forgotten and the Soul at any time. Also, if one of them is killed, it's game over for both.
* UndeadChild: Heavily implied to be Isaac's skeleton, after his corpse spent God knows how long locked inside the chest.
* WeCannotGoOnWithoutYou: If one character runs out of health, both characters die and the run is over. The are some exceptions, notably that by quickly switching back to the Forgotten after a Devil Deal that uses up all of the Soul's spirit/evil hearts, you can go on with the Soul being disabled until you get more of them.

[[/folder]]

!Monsters

[[folder:Flies]]
!Flies

!!In General
* AirborneMook: Making them immune to floor hazards, and allowing them to pass over obstacles.
* BigCreepyCrawlies: Even the weakest variety of fly (that you can actually fight) is still the size of one of Isaac's eyes.
* TheGoomba: Though these ones are killed by shooting at them with tears instead of jumping on their heads.

!!Black Fly/Attack Fly/Large Attack Fly/Ring Fly/Swarm Fly/Dart Fly/Hush Fly/Moter
[[quoteright:126:https://static.tvtropes.org/pmwiki/pub/images/fly3.png]]
-> Debut: ''The Binding of Isaac'' (Black Fly, Attack Fly, Moter)\\
''Rebirth'' (Ring Fly)\\
''Afterbirth'' (Swarm Fly, Dart Fly, Hush Fly)
* AsteroidsMonster: Moters split into two Attack Flies when killed.
* BeeAfraid: Swarm Flies and Dart Flies are likely bees or wasps given their colouring and buzzing sound.
* BulletproofHumanShield: As the Halo Of Flies and Pretty Fly powerups. The Forever Alone and Distant Admiration powerups spawn one capable of dealing good damage.
* EarlyBirdCameo: If you [[DownplayedTrope start your Isaac experience with Afterbirth +]], you may encounter Hush flies long before you fight [[FlunkyBoss Hush]] himself.
* EverythingsBetterWithSpinning: Ring Flies converge to form a spinning ring which tracks you as a group. As they're destroyed, they keep up the circle with wider gaps.
* MascotMook: The black variety is featured prominently in the artwork, and easily has the most related items.
* MookPromotion: If allowed to approach a pile of poop, a black fly consumes it and turns into a Pooter.
* ZergRush: Swarm Flies join into a clump and then rush you.

!!Level 2 Fly/Full Fly
[[quoteright:126:https://static.tvtropes.org/pmwiki/pub/images/level2fly.png]]
-> Debut: ''Rebirth''
* EliteMooks: As the name suggests, they are standard Flies, but larger and stronger.
* KaizoTrap: Full Flies release six bullets on death.

!!Pooter/Fat Fly (Super Pooter)
[[quoteright:100:https://static.tvtropes.org/pmwiki/pub/images/pooter.png]]
-> Debut: ''The Binding of Isaac'' (Pooter)\\
''Wrath of the Lamb'' (Fat Fly/Super Pooter)
* HighPressureBlood: One of the first enemies you'll see that can fire blood shots.
* {{Mook}}: Not any more dangerous than the normal flies.
* {{Retcon}}: The Fat Fly was renamed "Super Pooter" in ''Afterbirth+''.

!!Boom Fly/Red Boom Fly/Drowned Boom Fly
[[quoteright:144:https://static.tvtropes.org/pmwiki/pub/images/boomfly.png]]
-> Debut: ''The Binding of Isaac'' (Boom Fly, Red Boom Fly)\\
''Afterbirth'' (Drowned Boom Fly)
* ActionBomb: With the exception of the Red Boom Fly, they explode when killed.
* DisasterDominoes: An efficient way to clear a Boom Fly room is to kill one of them while they're all flying in a cluster. Doesn't work with Red Boom Flies, which shoot blood shots in 6 directions on death instead of exploding.

!!Sucker/Spit/Soul Sucker
[[quoteright:102:https://static.tvtropes.org/pmwiki/pub/images/sucker_5.png]]
-> Debut: ''The Binding of Isaac'' (Sucker)\\
''Wrath of the Lamb'' (Spit)\\
''Afterbirth†'' (Soul Sucker)
* ActionBomb: Spits.
* DisasterDominoes: In a room with several Spits, killing one while standing in the right direction will often cause a chain reaction of vomit bombs that kill the rest of them. The same goes for Soul Suckers, which will frequently kill every other Soul Sucker in the room.
* TakingYouWithMe: They release hard-to-dodge ranged attacks for Suckers, vomit bombs for Spits, and Brimstone lasers for Soul Suckers when killed.

!!Eternal Fly
[[quoteright:100:https://static.tvtropes.org/pmwiki/pub/images/eternalfly.png]]
-> Debut: ''Wrath of the Lamb''
* InvincibleMinorMinion: Until the monster or poop they orbit is destroyed, at least.
* MeaningfulName: As mentioned above, the Eternal Fly is, well, eternal, until the poop or monster they orbit is destroyed, turning it into an Attack Fly.

[[/folder]]

[[folder:Humanoid]]
!Humanoid

!!Gaper/Frowning Gaper/Flaming Gaper/Cyclopia/Greed Gaper/Blue Gaper
[[quoteright:199:https://static.tvtropes.org/pmwiki/pub/images/gaper_9.png]]
-> Debut: ''The Binding of Isaac'' (Gaper, Frowning Gaper)\\
''Afterbirth'' (Flaming Gaper, Cyclopia, Greed Gaper, Blue Gaper)
* CreepyChild: Gapers; They look much like your player character, but with TearsOfBlood and a creepy smile.
* {{Cyclops}}: Cyclopia, which move slower than Gapers but can fire blood tears.
* EliteMooks: Frowning Gapers to Gapers.
* EyeScream: Gapers have empty eye sockets filled with blood. The Cyclopia has only one eye in the middle of its head bleeding TearsOfBlood.
* InfernalRetaliation: Flaming Gapers move faster than normal. However, normal Gapers can't become Flaming Gapers by touching fire.
* LosingYourHead: All Gaper varieties can become Pacers or Gushers when killed.
* TearsOfBlood: Gapers have them on their faces. Cyclopias weaponize them in the form of creep and bullets.
* UniqueEnemy: In ''Afterbirth'', Blue and Greed Gapers only spawn as part of the Hush and Ultra Greed fights respectively. Averted in ''Afterbirth+'', since Greed Gapers can now spawn in item rooms and Blue Gapers can very rarely appear as regular enemies.

!!Pacer/Gusher/Black Globin's Body
[[quoteright:151:https://static.tvtropes.org/pmwiki/pub/images/pacer_7.png]]
-> Debut: ''The Binding of Isaac'' (Pacer, Gusher)\\
''Afterbirth'' (Black Globin's Body)
* EliteMooks: Gushers to Pacers. Black Globin's Bodies are even more elite, spawning only in Sheol and shooting spiders instead of bullets.
* HighPressureBlood: Gushers shoot out a fountain of blood from their necks, but only the occasional blood shot can actually deal damage.
* OverdrawnAtTheBloodBank: Gushers, as the name implies, have a constant stream of blood flowing from their necks.

!!Gurgle/Splasher
[[quoteright:100:https://static.tvtropes.org/pmwiki/pub/images/gurgle.png]]
-> Debut: ''Wrath of the Lamb'' (Gurgle)\\
''Rebirth'' (Splasher)
* LosingYourHead: Starting from ''Rebirth'', Gurgles have a chance to become Splashers when killed.
* SuperSpit: They hack up explosive Ipecac shots rather than the usual damaging blood.

!!Null
[[quoteright:100:https://static.tvtropes.org/pmwiki/pub/images/null.png]]
-> Debut: ''Rebirth''
* InvisibleMonsters: They [[InvisibilityFlicker fade in and out of sight]] while pursuing Isaac.

!!Horf/Psychic Horf
[[quoteright:114:https://static.tvtropes.org/pmwiki/pub/images/horf.png]]
-> Debut: ''The Binding of Isaac'' (Horf)\\
''Rebirth'' (Psychic Horf)
* EyeScream: Horf eye sockets are filled with blood.
* TearsOfBlood: Both have them, but only regular Horfs fire them.

!!Hopper/Flaming Hopper/Leaper
[[quoteright:114:https://static.tvtropes.org/pmwiki/pub/images/hopper.png]]
-> Debut: ''Binding of Isaac'' (Hopper, Flaming Hopper)\\
''Wrath of the Lamb'' (Leaper)
* BulletHell: Leapers shoot bullets in all four cardinal directions when they jump. If five end up in a room, be prepared to dodge.
* EliteMooks: Fire Hoppers and Leapers, the former being stronger and the latter shooting bullets.
* InfernalRetaliation: Hoppers move twice as fast, jump twice as far, and inflict more damage when they're on fire.
* MookPromotion: A Hopper that touches fire becomes a Flaming Hopper.
* ViolationOfCommonSense: Not only does every other enemy (or character, even) take damage themselves from fire, but Isaac's main combat strategy is attacking enemies with water. Despite that, they seem to have double health.

!!Maw/Red Maw/Psychic Maw
[[quoteright:172:https://static.tvtropes.org/pmwiki/pub/images/maw.png]]
-> Debut: ''The Binding of Isaac'' (Maw, Red Maw)\\
''Wrath of the Lamb'' (Psychic Maw)
* EliteMooks: Red Maws, with their lips stitched, can't shoot, but chase you pretty fast. They also [[{{Knockback}} get knocked away farther when hit]], offsetting their speed in terms of how easily you can keep them at bay (especially if you have a high rate of fire), but making it difficult to line up multiple shots against them.
** Psychic Maws also have their eyes stitched. They have a ThirdEye which shoots homing tears, and an Eternal Fly circling them.
** Maws themselves are basically Horfs, only with the ability to move, which eliminates the tactic of staying just outside of their range and shooting.
* TearsOfBlood: The Psychic Maw has this. The other Maws may have this, but it looks more like their eyes may have exploded out of their sockets instead.

!!Mr. Maw/Mr. Red Maw/Mr. Mine/Swinger
[[quoteright:175:https://static.tvtropes.org/pmwiki/pub/images/mr_maw.png]]
-> Debut: ''Wrath of the Lamb'' (Mr. Maw)\\
''Rebirth'' (Swinger)\\
''Afterbirth†'' (Mr. Red Maw, Mr. Mine)
* AquaticMook: Mr. Mines only appear on the Flooded Caves. Makes sense, considering they're meant to be sentient sea mines.
* AsteroidsMonster: Depending on whether you kill it by shooting it in the head or "body", Mr. Maw will spawn a Maw or Gusher, Mr. Red Maw a Red Maw or Gusher, and Swinger a Maw or Globin.
* DetachmentCombat: Mr. (Red) Maws and Mr. Mines will swing their heads out at you when you get close. Swingers are perpetually swinging, as their name suggests. Mr. (Red) Maw can also voluntarily separate into a (Red) Maw and a Gusher.
* EpicFlail: Their heads can be swung around like these.
* KaizoTrap: Mr. Mine doesn't have a body to break apart into, but fires six shots in all directions upon death.

!!Skinny/Crispy/Rotty
[[quoteright:181:https://static.tvtropes.org/pmwiki/pub/images/skinny_8.png]]
-> Debut: ''Rebirth'' (Skinny, Rotty)\\
''Afterbirth†'' (Crispy)
* BodyHorror: It has a more deformed appearance than most humanoid enemies.
* CriticalStatusBuff: Cripsies gain more movement speed the lower their health is. Given that they're on fire, they also slowly power themselves up.
* IncendiaryExponent: Crispies are on fire and eventually burn to death.
* PunnyName: "Skinny" not only refers to the folds of skin hanging off their faces but also sets them up as a FatAndSkinny duo with the Fatty.
* StrippedToTheBone: Non-fatal variant; killing a Rotty will sometimes cause it to become a Bony.

!!Bony/Black Bony
[[quoteright:114:https://static.tvtropes.org/pmwiki/pub/images/bony.png]]
-> Debut: ''Rebirth'' (Bony)\\
''Afterbirth'' (Black Bony)
* ActionBomb: Black Bonies explode on death.
* BallisticBone: Their main form of attack is tossing bones.
* DemBones: A walking skeleton.

!!Fatty/Flaming Fatty/Pale Fatty/Fat Sack/Blubber/Half Sack/Conjoined Fatty/Blue Conjoined Fatty/Stoney/Cross Stoney
[[quoteright:268:https://static.tvtropes.org/pmwiki/pub/images/fatty_5.png]]
-> Debut: ''Rebirth'' (Fatty, Pale Fatty, Fat Sack, Blubber, Half Sack)\\
''Afterbirth'' (Flaming Fatty, Conjoined Fatty, Blue Conjoined Fatty)\\
''Afterbirth†'' (Stoney, Cross Stoney)
* {{Acrofatic}}: While they're normally slow and bumbling, Fat Sacks have an attack where they jump high in the air and slam down. {{Averted}} with Stonies, who get out-of-breath after a while of chasing after Isaac.
* AmazingTechnicolorPopulation: Blue Conjoined Fatties, a rare enemy with a rather outlandish skin tone.
* DeadWeight: Fat Sacks are fat zombies.
* FatBastard: It's all in their names.
* {{Gasshole}}: Fatties can fart to push things away. Pale Fatties shoot ''blood'' when they do this.
* InfernalRetaliation: Flaming Fatties are faster than normal.
* InvincibleMinorMinion: Stonies behave just like Fatties but only die when every other enemy is killed.
* {{Kevlard}}: They're decently durable, and that probably comes from their immense fat.
* MultipleHeadCase: Conjoined Fatties have two heads. "Killing" it only destroys one head, reducing it to a regular Fatty.
* {{Nerf}}: Stonies were eventually changed to catch their breath every so often instead of chasing players without pause, as their release version made rooms too hard to clear.
* NightmareFace: The Fat Sack's face, with the empty eye sockets and TearsOfBlood.

!!Mulligan/Mulligoon/Mulliboom/Nest/Hive/Drowned Hive/Leper/Swarmer
[[quoteright:210:https://static.tvtropes.org/pmwiki/pub/images/mulligan_7.png]]
-> Debut: ''The Binding of Isaac'' (Mulligan, Mulligoon, Hive)\\
''Wrath of the Lamb'' (Mulliboom, Swarmer)\\
''Rebirth'' (Nest)\\
''Afterbirth'' (Drowned Hive)\\
''Afterbirth†'' (Leper)
* ActionBomb:
** Normal Mulligans puff up and explode into flies if they survive long enough and get cornered.
** Mulligoons replace the flies with a 4-way shot plus a troll bomb.
** Mullibooms come with bombs implanted in them and will charge and blow up on you.
** The Swarmer spawns a Bomb Fly upon death.
* AsteroidsMonster: As Lepers takes damage, small pieces of Leper Flesh will break off until the Leper turns into a Gusher.
* BodyHorror:
** The tumour-headed Mulligan grows more decayed as the flies inside it transform it into the Hive. From there, the Hive becomes a Swarmer, a rotten head filled with flies.
** Leper heads are mostly comprised of Fistula-like flesh barely held together by gristle. As pieces continue to break off, the Leper's slowly gets reduced piece-by-piece until it loses its head entirely and becomes a Gusher.
* IncurableCoughOfDeath: Has a very distinctive-sounding one when it spits up flies to attack you.
* MookMaker: Hives and Nests occasionally cough up flies and spiders respectively before spitting them at you, and Swarmers constantly spawn small flies as well as Pooters and Fat Flies when damaged. All varieties, other than the Mulliboom and Mulligoon, spawn various enemies when killed.
* TakingYouWithMe: Unlike his cousins, the Mulliboom (the one with a bomb stuck in his head) will rush straight at you and try to suicide-bomb you.

!!Globin/Gazing Globin/Dank Globin/Black Globin
[[quoteright:230:https://static.tvtropes.org/pmwiki/pub/images/globin.png]]
-> Debut: ''The Binding of Isaac'' (Globin, Gazing Globin)\\
''Afterbirth'' (Dank Globin, Black Globin)
* ArtificialBrilliance: They will move coordinately to trap you. Especially problematic in rooms with obstacles.
* EliteMooks: The versions with one eye are faster and have more health. Their meat pile also [[{{Knockback}} slides away diagonally]] a short distance to avoid being hit. Dank Globins spawn a spider and a puddle of tar whenever they collapse.
* PullingThemselvesTogether: When killed, they will become a pile of goo and then recover. Luckily, they will take less to kill next time.
* PunnyName: With "goblin" and "hemoglobin".
* TheLastOfTheseIsNotLikeTheOthers: Unlike its cousins, the Black Globin doesn't collapse into a pile of goo when killed. It instead separates into a head that [[BloodyMurder trails creep]] and a body that [[EnemySummoner spawns spiders]].
* WhyWontYouDie: Unless you finish off the pile of goo, this will happen. The main problem is attacking the goo while several others are chasing you.

!!Knight/Selfless Knight/Floating Knight/Bone Knight
[[quoteright:230:https://static.tvtropes.org/pmwiki/pub/images/knight.png]]
-> Debut: ''The Binding of Isaac'' (Knight, Selfless Knight)\\
''Rebirth'' (Floating Knight)\\
''Afterbirth'' (Bone Knight)
* AirborneMook: Floating Knight are flying Knight heads, ignoring pits and barriers.
* AttackItsWeakPoint: The front of them is solid bone or petrified flesh. The only way to actually damage it is to hit it in the back of its head, the exposed brain.
* BloodyMurder: Bone Knights trail damaging creep behind them, making it more difficult to target the exposed brain.
* EliteMooks: Its second variety chases the player instead of wandering aimlessly. They have a crying Isaac face instead of a brain on their back. Bone Knights are even more elite, leaving a trail of red creep as they walk.
* ShieldBearingMook: As customary, the solution is to flank it where its shield can't protect it.

!!Vis/Double Vis/Scarred Double Vis/Chubber
[[quoteright:230:https://static.tvtropes.org/pmwiki/pub/images/vis.png]]
-> Debut: ''The Binding of Isaac'' (Vis)\\
''Wrath of the Lamb'' (Double Vis, Chubber)\\
''Afterbirth'' (Scarred Double Vis)
* BodyHorror: They look like headless humans, only with a gaping hole on their chests that shoots Brimstone lasers in one or multiple directions.
* BloodyMurder: Fires what appears to be blood in a wide beam across the room it's in.
* TheComputerIsACheatingBastard: The Chubber is a variation that fires Lil' Chubby instead of a beam. Their Lil' Chubby can go through rocks and deal damage on the return trip, but yours can't do either.
* EliteMooks: As of the ''Wrath of the Lamb'' DLC, Vis has a second form which fires Brimstone both in front of and behind it. ''Afterbirth'' adds the Scarred Double Vis, which shoots in all four cardinal directions.
* HighPressureBlood: They shoot huge streams of blood that pass through all obstacles. In fact, they're probably the first enemy you'll see that can use Brimstone.

!!Baby/Angelic Baby
[[quoteright:106:https://static.tvtropes.org/pmwiki/pub/images/baby.png]]
-> Debut: ''The Binding of Isaac'' (Baby)\\
''Wrath of the Lamb'' (Angelic Baby)
* BodyHorror: Flying, blood-covered fetuses.
* EliteMooks: Has an angelic version that shoots a three-way spread shot instead of one bullet.
* FetusTerrible: Think of the familiar babies you can get, only shrieking and bloody.
* LightIsNotGood: The friendly and less harmful looking Angelic Baby is actually more dangerous due to it having a spread attack.
* TeleportSpam: Will frequently disappear into the nether before reappearing elsewhere a moment later.

!!Dople/Evil Twin
[[quoteright:154:https://static.tvtropes.org/pmwiki/pub/images/dople.png]]
-> Debut: ''The Binding of Isaac''
* {{Doppelganger}}: The EvilKnockoff variety.
* EliteMooks: The Evil Twin. Instead of looking like a meat puppet, it looks like a demon that can: fly, shoot a triple-shot and do more damage. Thankfully, its bullets travel slower and it has a fixed fire rate, giving you time to dodge and shoot.
* EnemyWithout: They mirror the player's movements, including shooting, but most rooms come with a mechanism with which to destroy them. There are also bombs, and praying that whipped shots will work.
* FlayingAlive: Dople has no skin.
* {{Foreshadowing}}: The appearance of these foreshadows the nature of [[spoiler:Isaac the boss]].
* MirrorMatch: They can perfectly mimic Isaac's movements and attack at the same time, though they cannot replicate certain tear properties.

!!Keeper/Hanger
[[quoteright:114:https://static.tvtropes.org/pmwiki/pub/images/keeper.png]]
-> Debut: ''Wrath of the Lamb''
* AdorableEvilMinions: The Keepers to Ultra Greed, as he will spawn them during his boss battle. The idea of small head creatures flopping clumsily around a boss arena doesn't sound too threatening, does it?
* AirborneMook: Hangers dangle from the ceiling, letting them pass over pits and obstacles.
* BanditMook: When they hit you, you lose three cents. Only two of those cents fall onto the ground to be picked up again.
* OrbitingParticleShield: Each Hanger has an Eternal Fly defending it.

!!Fred
[[quoteright:100:https://static.tvtropes.org/pmwiki/pub/images/mrfred.png]]
-> Debut: ''Wrath of the Lamb''
* BodyHorror: It's based on a baby with [[http://en.wikipedia.org/wiki/Harlequin-type_ichthyosis Harlequin-type ichthyosis]].
* WhackAMonster: They pop up in random areas of the room and attack either by firing an explosive shot or shooting a spray of bullets while diving through the air, before going underground and repeating the process.

!!Homunculus/Begotten
[[quoteright:195:https://static.tvtropes.org/pmwiki/pub/images/homunculus25.png]]
-> Debut: ''Rebirth''
* BodyHorror: Homunculus's warped facial features.
* BlackoutBasement: A Begotten will darken the room if it breaks free.
* BreakingTheBonds: They become significantly more dangerous when they break their chains and can pursue you.
* {{Expy}}: They start out trying to get at the player while chained but can break free and chase them, not unlike the [[Franchise/SuperMarioBros Chain Chomp]].
* InvisibleMonsters: Begotten becomes this once it breaks loose, similar to the Null. Fortunately, it also has the same InvisibilityFlicker.

[[/folder]]

[[folder:Worms and Grubs]]
!Worms and Grubs

!!Maggot
[[quoteright:100:https://static.tvtropes.org/pmwiki/pub/images/maggot.png]]
-> Debut: ''The Binding of Isaac''
* TheGoomba: Has no attacks, and just wanders around the room randomly.

!!Charger/Drowned Charger/Dank Charger
[[quoteright:175:https://static.tvtropes.org/pmwiki/pub/images/charger_5.png]]
-> Debut: ''The Binding of Isaac'' (Charger)\\
''Afterbirth'' (Drowned Charger)\\
''Afterbirth†'' (Dank Charger)
* DeadlyLunge: If they spot Isaac, they will open their mouths wide and speed towards him... exactly like Chub does. Dank Chargers also bounce around the room afterwards, but have to catch their breath before they can charge again.
* HighPressureBlood: What sets Drowned Chargers apart is that they burst into shots of blood when killed.
* OilSlick: Like a lot of Dank Depths enemies, Dank Chargers leave slippery oil everywhere they crawl.

!!Spitty/Conjoined Spitty
[[quoteright:132:https://static.tvtropes.org/pmwiki/pub/images/spitty.png]]
-> Debut: ''The Binding of Isaac''
* MultipleHeadCase: The conjoined version has a head on both ends, letting it spit blood in both directions simultaneously.

!!Leech/Kamikaze Leech/Holy Leech
[[quoteright:100:https://static.tvtropes.org/pmwiki/pub/images/leech.png]]
-> Debut: ''Wrath of the Lamb''
* ActionBomb: Kamikaze and Holy Leeches will explode on death.
* DeadlyLunge: Their main attack is to charge at Isaac at high speed.
* EliteMooks: Kamikaze to regular Leeches, and Holy to Kamikaze Leeches.
* OrbitingParticleShield: The Holy variant has an Eternal Fly guarding it.

!!Grub
[[quoteright:150:https://static.tvtropes.org/pmwiki/pub/images/grub.png]]
-> Debut: ''Rebirth''
* AsteroidsMonster: Each of its segments becomes a lesser variety of maggot on death.
* BossInMookClothing: Grubs are basically a stronger version of Larry Jr. In some boss fights against the latter, one of them is replaced with a Grub.

!!Round Worm/Nightcrawler/Tube Worm/Roundy/Ulcer
[[quoteright:181:https://static.tvtropes.org/pmwiki/pub/images/round_worm.png]]
-> Debut: ''The Binding of Isaac'' (Round Worm)\\
''Rebirth'' (Nightcrawler)\\
''Afterbith'' (Roundy, Ulcer)\\
''Afterbirth†'' (Tube Worm)
* BulletHell: The Tube Worm attacks by spraying a massive barrage of tears in the air, which fall near Isaac.
* FastTunnelling: All of them can submerge and re-emerge anywhere in the room quickly.
* MookMaker: Ulcers will spawn Dart Flies if left alone.

!!Para-Bite/Scarred Para-Bite/Cod Worm
[[quoteright:182:https://static.tvtropes.org/pmwiki/pub/images/parabite7.png]]
-> Debut: ''The Binding of Isaac'' (Para-Bite)\\
''Rebirth'' (Cod Worm)\\
''Afterbirth'' (Scarred Para-Bite)
* CounterAttack: Shooting at a Cod Worm while it is hiding in its shell will cause it to retaliate with a burst of tears.
* LosingYourHead: Scarred Para-Bites are Para-Bites with their heads ripped off.
* ShieldBearingMook: Cod Worms are entrenched in hard shells which they can retreat into at will.
* ZergRush: Para-Bites will bum-rush you endlessly, only briefly backing away to repeat the process.

!!Fistuloid
[[quoteright:75:https://static.tvtropes.org/pmwiki/pub/images/fistuloid.png]]
-> Debut: ''Afterbirth†''
* BodyHorror: As the name implies, it's a tiny Fistula.
* KaizoTrap: Fires a maggot towards Isaac on death.

[[/folder]]

[[folder:Spiders]]
!Spiders

!!Spider/Big Spider
[[quoteright:100:https://static.tvtropes.org/pmwiki/pub/images/spider.png]]
-> Debut: ''Wrath of the Lamb''
* AlienBlood: Inverted. The spiders in this game have red blood despite spiders in real life actually having pale blue blood.
* AsteroidsMonster: Big Spiders split into two after death.

!!Level 2 Spider/Ticking Spider
[[quoteright:134:https://static.tvtropes.org/pmwiki/pub/images/level2spider.png]]
-> Debut: ''Rebirth''
* ActionBomb: Ticking Spiders explode when killed.
* EliteMooks: Like the Level 2 Fly family, they are improved versions of standard spiders.

!!Baby Long Legs/Small Baby Long Legs/Crazy Long Legs/Small Crazy Long Legs
[[quoteright:246:https://static.tvtropes.org/pmwiki/pub/images/babylonglegs.png]]
-> Debut: ''Rebirth''
* MookMaker: Baby Long Legs make Spiders, while their Small counterparts create Sacks.
* WeaponizedOffspring: Both versions of the Baby Long Legs spawn spiders to attack Isaac with, though they don't seem too happy about it.

!!Wall Creep/Blind Creep/Rage Creep/The Thing
[[quoteright:222:https://static.tvtropes.org/pmwiki/pub/images/wallcreep_2.png]]
-> Debut: ''Rebirth'' (Wall Creep, Blind Creep, Rage Creep)\\
''Afterbirth†'' (The Thing)
* EyeScream: The Blind/Rage Creep and The Thing seem to be missing their eyes.
* HighPressureBlood: The Rage Creep fires a Brimstone laser when Isaac moves in front of it while The Thing creates a blood creep.
* ShoutOut: ''Film/TheThing1982''.
* WallCrawl: They can only move by crawling along the walls.

!!Trite/Ragling/Rag Man's Ragling/Blister
[[quoteright:159:https://static.tvtropes.org/pmwiki/pub/images/trite_6.png]]
-> Debut: ''Wrath of the Lamb'' (Trite, Ragling)\\
''Afterbirth'' (Rag Man's Ragling)\\
''Afterbirth†'' (Blister)
* DeadlyLunge: They normally hop around the room randomly, but if the player gets close, they will actively leap at the player; notably, when attacking, they can leap much farther than normal.
* GiantSpider: They're about the size of Isaac's head.
* ShoutOut: A Trite is a head-on four legs, with an eye-like mouth in the centre. In other words, [[VideoGame/TheLegendOfZeldaI a tektite.]]
* TearsOfBlood: The Trite.

[[/folder]]

[[folder:Other]]
!Other

!!Dip/Corn/Brownie Corn/Squirt/Dank Squirt/Dinga
[[quoteright:302:https://static.tvtropes.org/pmwiki/pub/images/dip.png]]
-> Debut: ''Rebirth'' (Dip, Squirt, Dinga)\\
''Afterbirth'' (Corn, Brownie Corn, Dank Squirt)
* AsteroidsMonster: Dingas split into two Squirts when killed, while Squirts split into two Dips. Dank Squirts split into two Clots instead.
* OneHitKill: Using Flush! will instantly kill any of them instantly, without turning them into "regular" poop.
* OneHitPointWonder: Corns and Brownie Corns are the weakest enemies in the game, dying in only one hit just with regular tear damage. Dips are only slightly tougher, taking two hits.
* StealthPun: Dips. (Which are made out of...)
* TalkingPoo: Actually, it's more like yelling poo.
* ToiletHumor: Regular poop lying everywhere not good enough for you? Now you can ''fight'' the poop!

!!Clot/Clotty/Mega Clotty/I. Blob/Ministro
[[quoteright:350:https://static.tvtropes.org/pmwiki/pub/images/clot_0.png]]
->Debut: ''The Binding of Isaac'' (Clot, Clotty)\\
''Wrath of the Lamb'' (I. Blob)\\
''Afterbirth'' (Mega Clotty)\\
''Afterbirth†'' (Ministro)
* AllYourPowersCombined: The I. Blob's projectiles, which are a combination of the Clot and Clotty.
* AsteroidsMonster: Mega Clotty will split apart into two Clotties on death.
* BlobMonster: Meat blob, tar blob, and... whatever the I. Blob is made of.
* BulletHell: They tend to shoot haphazardly, and very often, in every direction.
* TheCameo: Clot is very similar to VideoGame/{{Gish}}.
* EliteMooks: The I. Blob variant shoots projectiles in all eight directions. Ministro forgoes directional shots and does a Monstro-type spray attack.

!!Host/Red Host/Walking Host/Walking Red Host
[[quoteright:218:https://static.tvtropes.org/pmwiki/pub/images/host.png]]
-> Debut: ''The Binding of Isaac'' (Host)\\
''Wrath of the Lamb'' (Red Host)\\
''Rebirth'' (Walking Host, Walking Red Host)
* AttackItsWeakPoint: Only in the grey variation. To hit them, you must wait for them to expose the flesh under the skull. Moving them over spikes will also kill them.
* TheCameo: From a multiplayer flash game with the same name.
* NoSell: Regular Hosts are protected by their skull when they aren't firing. Trying to hit them does nothing. Trying to bomb them just causes them to make a troll face.
* ShieldBearingMook: The skulls the normal variety cover themselves with are impervious to pretty much any normal damage source.

!!Meatball
[[quoteright:100:https://static.tvtropes.org/pmwiki/pub/images/meatball.png]]
-> Debut: ''Afterbirth''
* BodyHorror: It's a sentient lump of mangled meat with an exposed skull that becomes a Host when damaged enough.
* HighPressureBlood: Its main attack is to spew a veritable fountain of bloody tears.

!!Brain/Poison Mind/Black Globin's Head/[=MemBrain=]
[[quoteright:200:https://static.tvtropes.org/pmwiki/pub/images/brain_06.png]]
-> Debut: ''The Binding of Isaac'' (Brain, [=MemBrain=])\\
''Afterbirth'' (Black Globin's Head)\\
''Afterbirth†'' (Poison Mind)
* AsteroidsMonster: [=MemBrain=] splits into two Brains when killed.
* BrainMonster: Of the "Just Brain" variety.
* LosingYourHead: As the name implies, Black Globin's Head is the head of a Black Globin. They behave like brains.
* UndergroundMonkey: Poison Minds move diagonally and leave green creep instead of red, but are otherwise identical to Brains.

!!Guts/Scarred Guts/Mama Guts
[[quoteright:125:https://static.tvtropes.org/pmwiki/pub/images/guts_1.png]]
->Debut: ''The Binding of Isaac'' (Guts, Mama Guts)\\
''Afterbirth'' (Scarred Guts)
* AsteroidsMonster: Like the [=MemBrain=], Mama Guts breaks apart into two Guts on death.
* BodyHorror: Does a rolling ball of organs sound pleasant to you?
* EliteMooks: Scarred Guts leave creep while they roll, and are slightly harder to kill.
* OrganAutonomy: Quite literally, they're organs that move on their own.
* RollingAttack: Guts and Scarred Guts only behavior is rolling around aimlessly on walls.

!!Poky/Slide/Wall Hugger
[[quoteright:268:https://static.tvtropes.org/pmwiki/pub/images/poky.png]]
* AntiFrustrationFeatures: Wall Huggers will have their spikes retracted for a few seconds upon entering a room, giving you time to get out of their way without taking damage from them.
* InvincibleMinorMinion: All varieties are immune to everything other than the Chaos Card. Pokies will die if the other enemies in the room are killed; Slides and Wall Huggers will not, and thus remain dangerous if you have to traverse the room again.
* SpikesOfDoom: Mobile blocks covered in dangerous spikes.

!!Stone Grimace/Vomit Grimace/Cross Grimace/Gaping Maw/Broken Gaping Maw/Turret Grimace/Stone Eye/Brimstone Grimace
[[quoteright:208:https://static.tvtropes.org/pmwiki/pub/images/stone_grimace.png]]
* DisasterDominoes: Vomit Grimaces are often found together with Boom Flies, which are not immune to the vomit projectiles.
* HighPressureBlood: Brimstone Grimaces can shoot blood in a strong beam.
* InvincibleMinorMinion: They usually shut off after all other enemies in a room are dead, however.
* LivingStatue: Statue heads which fire projectiles.
* ObviousRulePatch: The Broken Gaping Maw was originally created for one room, for only one purpose; because the room used to house four standard Gaping Maws in the center, and a player character with flight and sufficiently low speed could become trapped forever in the center of their combined gravity. The Broken Gaping Maw shuts off periodically, allowing the player to escape. Booster Pack #5 made them far more ubiquitous.
* VacuumMouth: Gaping Maws are constantly breathing in, which will suck Isaac and other things towards it.

!!Boil/Gut/Sack/Blue Boil/Walking Boil/Walking Gut/Walking Sack/Gush
[[quoteright:188:https://static.tvtropes.org/pmwiki/pub/images/boil_0.png]]
-> Debut: ''The Binding of Isaac'' (Boil)\\
''Wrath of the Lamb'' (Gut, Sack, Walking Boil, Walking Gut)\\
''Rebirth'' (Walking Sack)\\
''Afterbirth'' (Blue Boil)\\
''Afterbirth†'' (Gush)
* EliteMooks: As of ''Wrath of the Lamb'', there is the Gut, which shoots green bombs, much like Sloth. As well as mobile versions of each.
* HealingFactor: The non-mobile versions slowly regenerate over time when damaged. However, they spawn with less-than-full HP and can't attack until they've reached their maximum health. [[ShowsDamage Their health is directly proportional to their size.]]
* MookMaker: Sacks are made of spider silk, which spits out spiders. It, too, has a mobile version.
* OilSlick: Gush is unique because it does no damage, it just leaves oil in a growing radius around it. It can make it hard to dodge other enemies, though.

!!One Tooth/Fat Bat
[[quoteright:194:https://static.tvtropes.org/pmwiki/pub/images/onetooth.png]]
-> Debut: ''Rebirth'' (One Tooth)\\
''Afterbirth'' (Fat Bat)
* ArtificialBrilliance: The Fat Bat actively tries to avoid your shots as it approaches you. However, it's not quite fast enough to dodge effectively.
* BatOutOfHell: Doesn't look very menacing in comparison to most examples, but it attacks all the same.
* DeadlyLunge: One Tooth will dash at the player if it gets close.
* IncrediblyDurableEnemies: The Fat Bat's slow speed is offset by its [[{{Kevlard}} abnormally large health pool]] and erratic movement, especially for an enemy that appears starting from the Caves.

!!Dukie
[[quoteright:100:https://static.tvtropes.org/pmwiki/pub/images/dukie.png]]
-> Debut: ''Afterbirth''
* MookMaker: Spawns Dart Flies as it bounces around the room.
* PunnyName: A play on the Duke of Flies, who they resemble, and a slang word for poop.

!!Butt Licker
[[quoteright:100:https://static.tvtropes.org/pmwiki/pub/images/buttlicker.png]]
-> Debut: ''Wrath of the Lamb''
* AsteroidsMonster: The segments split and act independently after one of them dies.
* ToiletHumor: Besides constantly tossing each other's salads, they'll ''eat poop''. Doesn't get much more toilet-humorous than that.

!!Eye/Bloodshot Eye
[[quoteright:124:https://static.tvtropes.org/pmwiki/pub/images/eye21.png]]
-> Debut: ''The Binding of Isaac''
* EliteMooks: The Bloodshot Eye looks like a red (white in the original) eyeball and nothing else. It shoots Brimstone lasers instead of electrical beams.
* EyeBeam: Their entire schtick.
* EyeScream: Being giant eyes, it's inevitable.
* FacelessEye: They're giant eyes that are found just lying on the ground.
* HighPressureBlood: Bloodshot Eyes fire Brimstone lasers.
* IronicName: In the original, the Bloodshot Eye simply looked like a normal white eyeball, while the regular Eye looked bloodshot with various veins surrounding them. This was reversed in Rebirth.
* StealthPun: Bloodshot Eye is an eye that shoots blood.

!!Mask + Heart
[[quoteright:110:https://static.tvtropes.org/pmwiki/pub/images/maskplusheart.png]]
-> Debut: ''Wrath of the Lamb''
* AttackItsWeakPoint: The Mask is completely immune to all damage. The Heart isn't.
* OrganAutonomy: The hearts are not defenseless: they will attempt to run away from Isaac and will defend themselves with a four-way blood burst if he gets too close.

!!Death's Head/Dank Death's Head/Flesh Death's Head
[[quoteright:172:https://static.tvtropes.org/pmwiki/pub/images/deathshead.png]]
-> Debut: ''Rebirth'' (Death’s Head)\\
''Afterbirth'' (Dank Death’s Head, Flesh Death’s Head)
* HighPressureBlood: Flesh Death's Heads will burst into shots of blood when they die, either from manual shooting or from the room being otherwise cleared.
* InvincibleMinorMook: The standard variety keep bouncing around the room until every kill-able enemy in it is dead. They aren't immune to the Chaos Card, but why would you waste a Chaos Card on one? Dank and Flesh varieties can be killed like any normal enemy; Dank Death's Heads must be destroyed to clear a room, while Flesh Death's Heads will also automatically die if the other enemies in the room are killed.
* TakingYouWithMe: Flesh Death's Heads explode into 6 bullets launched in all directions when killed, either directly or by destroying all other enemies in the room.

!!Lil' Haunt/Wizoob/Red Ghost
[[quoteright:172:https://static.tvtropes.org/pmwiki/pub/images/lilhaunt.png]]
-> Debut: ''Rebirth'' (Lil' Haunt, Wizoob)\\
''Afterbirth'' (Red Ghost)
* {{Expy}}: With their attack method and name, Wizoobs are clearly based off of the original [[VideoGame/TheLegendOfZelda Wizrobes]].
* HighPressureBlood: The Red Ghost's Brimstone laser attack.
* WhackAMonster: Wizoobs and Red Ghosts will pop up near Isaac, fire off an attack, and then disappear for an extended period of time before repeating the process.

!!Imp
[[quoteright:100:https://static.tvtropes.org/pmwiki/pub/images/imp.png]]
-> Debut: ''Afterbirth''
* ArtificialBrilliance: The only enemy in the game to make an active effort of anticipating incoming shots and dodging out of the way.
* TeleportSpam: Teleports to a random spot in the room after firing 3 shots.
* UndergroundMonkey: A Sheol variant of Baby enemies.

!!Mom's Hand/Mom's Dead Hand
[[quoteright:350:https://static.tvtropes.org/pmwiki/pub/images/momshand.png]]
-> Debut: ''Rebirth'' (Mom’s Hand)\\
''Afterbirth'' (Mom’s Dead Hand)
* EvilLaugh: Mom's laugh is the cue that they're in the current room.
* MookBouncer: In addition to dealing damage, Mom's Hand also pulls you back to the starting room of the floor if they grab you. This can actually be helpful for a quick trip back to the starting room on a dead end, if you have the hearts to spare. Not so with the Dead variety, which simply deals damage.
* WallMaster: They hide on the ceiling of rooms, eventually diving down on Isaac.

!!Tumor/Psy Tumor/Camillo Jr.
[[quoteright:256:https://static.tvtropes.org/pmwiki/pub/images/tumor.png]]
-> Debut: ''Rebirth''
* BulletHell: They shoot haphazardly in all directions at irregular intervals. Additionally, they shoot more frequently at low health, so fighting multiple Tumors can get messy very quickly.
* EyeBeams: Camillo Jr. attacks with lasers rather than bullets.
* ShoutOut: Camillo Jrs. have their name based off of [[VideoGame/{{Kirby}} Kracko Jr.]] However, they look more like regular Kracko, so the Jr. is likely there to make the inspiration clearer.
* TurnsRed: All varieties will shoot more frequently as they take damage.

!!Nerve Ending/Nerve Ending II
[[quoteright:106:https://static.tvtropes.org/pmwiki/pub/images/nerveending_0.png]]
-> Debut: ''Rebirth'' (Nerve Ending) \\
''Afterbirth†'' (Nerve Ending II)
* BodyHorror: It's a GIANT DISEMBODIED NERVE ENDING!
* CombatTentacles: Nerve Ending II is one.
* {{Expy}}: The Nerve Ending II's color scheme and method of attack bear more than a passing resemblance to a [[VideoGame/{{StarcraftII}} Spine Crawler]].
* JokeCharacter: Nerve Ending doesn't attack, it just blocks bullets. By the time you're far enough into a run to see these guys, that's already not a problem. Nerve Ending II actually does attack, though (it swats at you), which may take some players by surprise the first time they get near them. It can also replace regular Nerve Endings in room layouts, forcing you to stay on your toes.

!!Lump/Tar Boy
[[quoteright:200:https://static.tvtropes.org/pmwiki/pub/images/lump_5.png]]
->Debut: ''The Binding of Isaac'' (Lump) \\
''Afterbirth†'' (Tar Boy)
* FastTunnelling: They can move around "underground" very quickly.
* TeleportInterdiction: Tar Boys can only pop up in spots with oil on the ground. However, they can make oil with their shots and often spawn in rooms with Gushes that can makes lots of oil for them.
* WhackAMonster: When approached, they will fire in the player's general direction to distract them, then go underground and pop up in another part of the room.

!!Oob/Black Maw
[[quoteright:210:https://static.tvtropes.org/pmwiki/pub/images/oob.png]]
-> Debut: ''Rebirth''
* ActionBomb: Black Maw explodes when killed and can spawn Kamikaze Leeches, which also explode.
* EnemySummoner: Both are capable of spawning more enemies: Oob summons Brains, while Black Maw spawns Leeches.
* ShoutOut: They are directly taken from ''VideoGame/SuperMeatBoy'', another Edmund [=McMillen=] game. The former was an enemy, the latter was an obstacle.

!!Portal
[[quoteright:97:https://static.tvtropes.org/pmwiki/pub/images/portal_6.png]]
-> Debut: ''Afterbirth†''
* {{Foreshadowing}}: They are identical in appearance to the entrance to the Void, [[spoiler:which is the manifestation of Isaac's mental breakdown]].
* MookMaker: Their only purpose is to spawn random enemies until destroyed.
* {{Nerf}}: Shortly after release, Portals were changed to expire on their own after spawning 1-5 enemies instead of spitting out enemies indefinitely until destroyed.
* NonStandardCharacterDesign: Those spinning vortexes are definitely not mutilated humanoids like most of the other enemies, nor bugs, nor do they even fit the "demonic" category too well. [[spoiler:This is suggesting that they are something "outside" of the narrative Isaac made up -- they represent his mind breaking down.]]

!!Mushroom
[[quoteright:60:https://static.tvtropes.org/pmwiki/pub/images/mushroom.png]]
-> Debut: ''Afterbirth†''
* IncrediblyDurableEnemies: They have a ''very'' large health pool, especially for an enemy that can show up as early as the Caves. Attacking while their faces are exposed deals higher damage.
* MushroomMan: It's a mushroom with a face, though that's hardly unusual compared to some of the other enemies present.

[[/folder]]

!!Bosses

[[folder:Basement, Cellar, Burning Basement]]
!!Monstro
[[quoteright:132:https://static.tvtropes.org/pmwiki/pub/images/monstro.png]]
->Debut: ''The Binding of Isaac''
* AsteroidsMonster: His Eternal form in the ''Eternal Edition'' splits as it takes damage. The smaller forms shoot less bullets, however.
* BodyHorror: He's some kind of deformed head, lacking a nose and most of his teeth, and features a prominent harelip.
* ClippedWingAngel: The grey Champion version is bigger with more health, but it can't use the leap attack of the normal version, making it far easier to circle around and shoot with no risk to yourself. Even in pairs, it's much less of a threat.
* DegradedBoss: After the game is beaten six times, he'll start showing up in non-boss rooms occasionally.
* TheDragon: Oddly enough, Monstro will occasionally appear before an Ultra Greed battle.
* DualBoss: The red Champion version is two smaller Monstros.
* EasterEgg: One Active item, Monstro's Tooth, calls in the aforementioned boss to body-slam enemies. On the chance that you end up getting it as one of your first items, [[MirrorMatch guess which boss you]] [[AvertedTrope can't use it against.]]
* HeelFaceTurn: The Monstro's Tooth item lets you summon him to crush your enemies.
* WarmUpBoss: One of the less complicated bosses and one of the most likely to run into first. Many prefer getting zero-damage boss battles on Monstro to increase the likelihood of Devil Deals spawning.

!!Larry Jr.
[[quoteright:157:https://static.tvtropes.org/pmwiki/pub/images/larryjr.png]]
->Debut: ''The Binding of Isaac''
* AsteroidsMonster:
** Not so much as other bosses, but if the middle section is killed first in a 5-segment one, it will split into two more versions with just two segments.
** Much easier to happen with his Eternal counterpart in the ''Eternal Edition'', where a broken-off segment can last as just a head and can regenerate segments.
* TheCameo: A smaller version of [[VideoGame/MeatBoy Larrie's Lament]].
* DegradedBoss: The most common boss enemy to find in [[spoiler:The Womb]].
* DualBoss: Easily the most common one; his standard fight in the Basement is always two of him. ''Afterbirth'' occasionally mixes things up with a single very long Larry Jr., but he'll likely be splitting into multiple Larries over the course of the fight anyway because of how the boss works.
* FluffyTheTerrible: It's a blood-coated demonic giant maggot, yet has one of the most cutesy-sounding names in the game.
* KingMook: As of ''Wrath of the Lamb'', smaller enemies similar to it appear.
* SegmentedSerpent: Larry Jr. is composed of several body segments that have individual HP bars and can be destroyed separately. Killing a segment in the middle of its body can cause it to split into two individual worms, but a segment cannot survive if it isn't attached to another.
* WarmUpBoss: Shares this with Monstro. It can't even shoot at you (except for the green champion version), but its movement patterns can be erratic thanks to the poop it leaves behind.

!!The Duke of Flies
->Debut: ''The Binding of Isaac''
[[quoteright:134:https://static.tvtropes.org/pmwiki/pub/images/dukeofflies.png]]
* BodyHorror: It's safe to assume that the only reason he can move around is that of the flies that have infested his bloated body. He also lacks eyes of any kind.
* DegradedBoss: After unlocking "Everything's Terrible!"
* FlunkyBoss: "Attacks" by creating tons of flies.
* MookMaker: As its name implies, it creates flies.
* KingMook: To the Dukies.
* TakingTheBullet: Spawned flies circle the Duke until he commands them to attack you, letting them soak up your shots.

!!Gemini (Contusion & Suture)
[[quoteright:139:https://static.tvtropes.org/pmwiki/pub/images/gemini.png]]
->Debut: ''The Binding of Isaac''
* BigGuyLittleGuy: Contusion is the big twin, Suture is the little one.
* BrainsAndBrawn: Suture is the Brains while Contusion is the Brawn.
* BullfightBoss: Contusion can tire out after a few moments of charging the player. If he is killed first, Suture will turn red, give chase, and never tire out.
* DualBoss: Contusion, who walks towards the player and charges at them periodically, and Suture, who shoots bullets.
* FetusTerrible: Both of them seem to represent fetuses, even having an umbilical cord attached to each other. Suture even moreso.
* HeelFaceTurn: The Gemini zodiac sign gives you a friendly copy of Suture who attacks your enemies.
* PolarOppositeTwins: Contusion is aggressive and chases you; Suture looks calm and makes ranged attacks until you kill his brother, at which point it charges at you.
* TurnsRed: What Suture does when Contusion dies.

!!Steven
[[quoteright:100:https://static.tvtropes.org/pmwiki/pub/images/steven.png]]
->Debut: ''The Binding of Isaac''
* BonusBoss: After being unlocked, occasionally replaces Gemini.
* TheCameo: Steven is from ''VideoGame/TimeFcuk''.
* HeelFaceTurn: the Little Steven item summons a friendly version of Steven who shoots at enemies, and is almost always dropped by this boss (except when it drops the "Steven" item instead, which is just a damage upgrade).
* LastDitchMove: Both parts of Steven shoot bullets in all directions when they die.
* TurnsRed: When their aggregate health reaches 1/3, the small one detaches and turns red just like Gemini's.

!!Fistula
[[quoteright:134:https://static.tvtropes.org/pmwiki/pub/images/fistula.png]]
->Debut: ''The Binding of Isaac''
* AsteroidsMonster: It has three distinct sizes. Large Fistula splits into four medium Fistulae (three for the champion version) on death, each of which splits into two small Fistulae. Small Fistula either spawns a Charger or a Boom Fly, depending on the version fought.
* BodyHorror: It's named for a real-life chunk of BodyHorror in which organs try to absorb each other.
* DegradedBoss:
** Appears as this in later stages. Most of the time, though, it will already be broken down to its second or third stage.
** In ''Rebirth'', the boss is now a Chapter One boss.

!!Widow
[[quoteright:141:https://static.tvtropes.org/pmwiki/pub/images/widow.png]]
->Debut: ''Wrath of the Lamb''
* BodyHorror: She's made out of a head with four eyes, leg bones, and toes.
* FlunkyBoss: Not only does she spawn spiders directly, but she can also spawn MookMaker Sacks! And that's not even getting into the ones that can spawn bigger AsteroidsMonster spiders or other kinds of Boils.
* GiantSpider: She's a larger version of the Trites. Considering that those are already the size of Isaac, it makes for an intimidating boss fight!
* GlassCannon: Relatively low HP for a boss, but moves unpredictably and spits out the equally unpredictable spiders, making her harder to beat without taking any damage than most bosses early on.
* KingMook: To the spiders.
* PinkMeansFeminine: One of her champion colors is pink, and she's one of the few female bosses.
* RushBoss: She's a fragile boss, but if you don't kill her quickly, you'll get overwhelmed by the spiders she summons and the speed she moves at.
* StealthPun: One of her champion colours is black. [[spoiler:A Black Widow spider.]]

!!Pin
[[quoteright:110:https://static.tvtropes.org/pmwiki/pub/images/pin.png]]
->Debut: ''Wrath of the Lamb''
* SandWorm: A Sand ''Tapeworm'' at that, but nevertheless, it's a giant worm creature that attacks by burrowing through the earth and diving out of the ground.
* SegmentedSerpent: Like Larry Jr., Pin has multiple body segments that take damage separately. However, what separates Pin is that each segment does not a separate health bar, which will cause it to take significantly more damage from piercing and explosive attacks.
* TacticalSuicideBoss: It is not immune to its exploding Ipecac projectiles, and due to a quirk in hit detection, can actually damage itself with them when it begins to bury underground. The dark grey one averts it, replacing the bombs with bullets.
* WarmUpBoss: Competing with Larry Jr. and Monstro for the easiest boss in the game; Relatively low health, a large hitbox, extremely predictable and avoidable attacks, and he's not immune to his own projectiles. Many players feel silly if they take ''any'' damage to this boss at all, let alone die to him.

!!Gurdy Jr.
[[quoteright:115:https://static.tvtropes.org/pmwiki/pub/images/gurdyjr.png]]
->Debut: ''Wrath of the Lamb''
* AchillesHeel: Slow effects will kill Gurdy Jr.'s momentum and stop her charge attack in its tracks.
* BullfightBoss: Her main attack is to charge at the player, bouncing off of anything she happens to hit.
* DualBoss: The blue version is two smaller Gurdy Jr.'s.
* {{Expy}}: Of Gurdy. Formerly, she would only appear as a DegradedBoss; see MissingSecret below.
* HeelFaceTurn: The Lil' Gurdy item gives you an even smaller version of this boss, who uses its charging attack.
* MissingSecret: Before version 1.2, she would only appear as a DegradedBoss.

!!Blighted Ovum (Contusion and Suture, again)
[[quoteright:133:https://static.tvtropes.org/pmwiki/pub/images/blightedovum.png]]
->Debut: ''Wrath of the Lamb''
* BackFromTheDead: Contusion is now a zombie, and is accompanied by the ghost of his (formerly) conjoined brother, Suture.
* BodyHorror: Contusion has a gash on his head where his eye once was, lacks a lower jaw, and is either covered in blood or has no skin on his lower body.
* BullfightBoss: Contusion, much like his living counterpart, except he never tires, gets progressively faster, and leaves a trail of red creep behind him.
* InvincibleMinorMinion: Suture's ghost can't be harmed; the only way to get rid of him is to get rid of his brother.
* {{Nerf}}: In the original game, both parts of the Blighted Ovum would fire bullets in all directions upon death. This ability was removed in ''Rebirth'' and given to Steven.
* WaveMotionGun: The ghostly Suture fires Brimstone if you stand to the left or right of it.

!!Gurglings/Turdlings
[[quoteright:111:https://static.tvtropes.org/pmwiki/pub/images/gurglings.png]] [[quoteright:134:https://static.tvtropes.org/pmwiki/pub/images/turdlings.png]]
-> Debut: ''Rebirth'' (Gurglings)\\
''Afterbirth'' (Turdlings)
* BullfightBoss: They'll charge you if you get in their line of sight.
* CreepyTwins: When fought as a pair. Identical ''and'' dangerous.
* DegradedBoss: They appear as regular enemies as early as the Caves, and don't even get a health bar. On the other hand, they constantly leave behind damaging trails of creep (as opposed to only doing so when charging) and shoot six-way blood bursts rather than spawning flies, making them actually slightly ''more'' dangerous than the boss version.
* DualBoss: They appear as a pair.
* DungFu: Turdlings leave behind brown creep when they charge.
* EnfantTerrible: They seem to be even younger versions of Gurdy Jr.
* FlunkyBoss: One of the major differences between Turdlings and Gurglings is that Turdlings spawn several Corn Dips after their charge attack.
* PaletteSwap: Turdlings are a rare poop-themed version of the Gurglings, possessing similar attacks.

!!Dingle/Dangle
[[quoteright:112:https://static.tvtropes.org/pmwiki/pub/images/dingle.png]] [[quoteright:138:https://static.tvtropes.org/pmwiki/pub/images/dangle.png]]
-> Debut: ''Rebirth'' (Dingle)\\
''Afterbirth'' (Dangle)
* AdorableEvilMinions: His Squirts.
* BullfightBoss: One of his attacks is to charge at you three times in succession, occasionally leaving a pile of poop on the first charge. He scrunches up just before the charge and gets pooped ([[JustForPun heh]]) after the third charge, allowing you to get damage in.
* CuteIsEvil: He's probably the cutest boss in the game, and not in an
"ugly cute" way. But just like every other boss, he still wants you dead.
* DegradedBoss: Often appear in the Womb. Brownie always becomes a Dangle after he dies.
* DungFu: Besides being made of poop, he will also frequently summon Squirts or leave more poop laying around.
* NobodyPoops: Averted, obviously.
* NotSoInnocentWhistle[=/=]EnemySummoner: He occasionally will whistle innocently (complete with a music note hovering above his head), before one to three Squirts appear beside him to fight. This is immediately followed by a bullet spread attack.
* OneHitKill: Using Flush! will kill him instantly.
* PaletteSwap: Dangle is one of Dingle, possessing the same attacks but with slightly different properties. He's essentially a Champion variation with his own title screen.
* ToiletHumor: It's a giant adorable poop. Dangle takes it a step further by shooting ''corn'' at you.

!!The Haunt
[[quoteright:156:https://static.tvtropes.org/pmwiki/pub/images/thehaunt.png]]
-> Debut: ''Rebirth''
* AdorableEvilMinions: The Lil' Haunts that surround him are this.
* BedsheetGhost: What's underneath its sheet is quite a bit scarier, however.
* FlyingFace: That rips itself open to reveal a [[SkullForAHead skull]] when its minions are dealt with.
* FlunkyBoss: He is surrounded by three Lil Haunts which attack before he does. First one attacks, then the other two do. He's invulnerable until they're dead and he moves to the top of the room. His black Champion version spawns spiders instead of shooting Brimstone.
* {{Expy}}: Very closely resembles a [[Franchise/{{Mario}} Boo]].
* HeelFaceTurn: The Lil' Haunt item gives you a friendly Lil' Haunt who chases your enemies.
* {{Intangibility}}: Until his minions are dead, the Haunt is untouchable.
* KingMook: To the Lil' Haunts.
* NightmareFace: Once you kill his minions, he rips off his face to reveal his skeleton.
* NoFairCheating: He normally paces from side to side along the top edge of the screen, shooting downwards. If you try to move to the top where he can't shoot you, he'll immediately charge at you to cause damage. Which ''hurts like '''crazy.'''''
* OurGhostsAreDifferent: This one has a skeleton. Which he'll gladly show to you.
* ThePawnsGoFirst: Sends his Lil' Haunt minions to attack you while he himself remains intangible. When they go down, then he fights you.
* WaveMotionGun: In his second phase, he'll fire Brimstone downwards as he strafes along the top of the screen. It has minimal telegraphing compared to most Brimstone attacks, so stay on your toes.

!!Rag Man
[[quoteright:150:https://static.tvtropes.org/pmwiki/pub/images/ragman.png]]
->Debut: ''Afterbirth''
* AlienBlood: His blood is purple.
* FlunkyBoss: He'll occasionally detach his head. Not only does the head move and attack independently from his main body, but if it isn't destroyed quickly, it turns into a Rag Man's Ragling.
* HealThyself: Aside from the regrowing heads thing, Rag Man possesses the unique ability to revive the Raglings created from his heads. This also restores a small amount of his HP.
* LosingYourHead: Detaching his head doesn't seem to bother him too much, especially since it turns into a Ragling and he can simply grow a new one.
* {{Mummy}}
* PsychicPowers: His primary attacks are homing psychic blasts.

!! Little Horn
[[quoteright:100:https://static.tvtropes.org/pmwiki/pub/images/littlehorn.png]]
->Debut: ''Afterbirth''
* GetBackHereBoss: Spends a lot of the fight teleporting away from the player, often leaving a Troll Bomb behind. It also flees from the player if approached.
* HomingProjectile: It fires large homing projectiles that will track you forever until you destroy them with your own attacks.
* PlayingWithFire: The orange Champion version spits out burning Troll Bombs instead of the black homing projectiles, which deal contact damage and leave behind a damaging fire upon detonation.
* PortableHole: Can make these to teleport itself around the room, teleport Troll Bombs around the room, or to send straight at you so that you will fall in and take damage.
* ScrewThisImOuttaHere: When his health gets depleted, instead of dying, he retreats into one of his portable holes.
* TacticalSuicideBoss: Has a tendency of teleporting into its own Troll Bombs. The boss room also tends to have fires, into which Little Horn will run if you herd him in that direction.
* ThinkingUpPortals: Can open up two holes that are linked to each other, either to teleport itself around the room or as a lead up to the following trope.
* ThrowDownTheBomblet: Attacks with Troll Bombs by opening a pair of portals between his location and the player and throwing one in.

[[/folder]]

[[folder:Caves, Catacombs, Flooded Caves]]

!!Gurdy
[[quoteright:190:https://static.tvtropes.org/pmwiki/pub/images/gurdy.png]]
->Debut: ''The Binding of Isaac''
* BodyHorror: She's what can only be described as a mountain of flesh and organs, with a smiling face at the top.
* DamageSpongeBoss: The bulkiest boss in the Caves, having more health than some of the later bosses.
* DegradedBoss: Interestingly, the weaker version attacks very differently, charging and firing circular waves of bullets. Contrast with the other bosses made into minibosses, who are more or less identical to their original version, but weaker. ''Wrath of the Lamb'' separates the degraded form into a different boss: Gurdy Jr. [[spoiler:But TheVeryDefinitelyFinalDungeon DOES feature Gurdy as a normal Degraded Boss.]]
* FlunkyBoss: Spawns Flies and Boils to assist her. Her Champion version ''only'' spawns enemies and never fires at you.
* StationaryBoss: She always stays in the middle of the room. Even if you push her away with a fear effect, she'll move back into position when it wears off.
* WakeUpCallBoss: When it comes to the pre-''Wrath of the Lamb'' bosses who gave new players trouble, Gurdy is the most infamous.

!!Peep
[[quoteright:149:https://static.tvtropes.org/pmwiki/pub/images/peep.png]]
->Debut: ''The Binding of Isaac''
* AmbiguouslyHuman: He's the most human-looking of the monsters, save for the fact that his eyes pop out and his urine-based powers.
* EyeScream: It detaches its eyeballs when its HP starts getting low. They block your shots and will inflict CollisionDamage on you if you touch them. Oh! And [[EyesAreUnbreakable they're indestructible]] until you kill their original owner (unless you have the Little Horn passive item).
* DetachmentCombat: His eyes will fly off as he takes damage, becoming wall-bouncing obstacles.
* ExtraEyes: His Eternal counterpart in the ''Eternal Edition'' has ''six'' eyes. Yes, they can all detach, but they're also destructible.
* FatBastard: Obese, and one of the bosses in the game.
* HeelFaceTurn: Not the boss itself, but The Peeper item gives you a floating eyeball familiar that moves the same way as Peep's eyes.
* MeaningfulName:
** Pronounce the second "p" [[ItIsPronouncedTroPay as though you were saying the letter "p"]].
** There's also the fact that "peep" can mean to look at something, and he attacks you with his eyes.
* PsychopathicManChild: He smiles during the fight and cries after being defeated.
* ToiletHumor: Attacks with urine.
* UrineTrouble: His main form of attack.

!!Chub
[[quoteright:175:https://static.tvtropes.org/pmwiki/pub/images/chub.png]]
->Debut: ''The Binding of Isaac''
* BullfightBoss: Her main form of attack is to charge at Isaac with jaws wide open.
* DegradedBoss: Another common boss enemy to find in The Depths and [[spoiler:The Womb]].
* FeedItABomb: Has the exact same weakness as Dodongo of ''VideoGame/TheLegendOfZelda'' fame, though she can also be beaten by regular attacks.
* FlunkyBoss: She can spawn various Maggots from her behind.
* HeelFaceTurn: The Little Chub item gives you a friendly one that charges at your enemies.
* KingMook: To the maggots.

!!C.H.A.D.
[[quoteright:148:https://static.tvtropes.org/pmwiki/pub/images/chad18.png]]
->Debut: ''The Binding of Isaac''
* BonusBoss: Occasionally replaces Chub once unlocked.
* TheCameo: C.H.A.D. is a boss from ''Super VideoGame/MeatBoy''. Dropping the item Little C.H.A.D. on defeat references his post-fight cutscene from the above.
* HeelFaceTurn: The Little C.H.A.D item gives you a friendly C.H.A.D. who "gives kisses" (half red hearts) every few rooms.
* ObliviouslyEvil: C.H.A.D. is charging at you not out of spite, but because he wants a hug.
* TurnsRed: As C.H.A.D. takes damage, he gets smaller and faster but no less dangerous.

!!The Husk
[[quoteright:107:https://static.tvtropes.org/pmwiki/pub/images/thehusk.png]]
->Debut: ''Wrath of the Lamb''
* BackFromTheDead: The Duke of Flies' rotting corpse.
* FlunkyBoss: Spawns even MORE flies than the Duke does, with some spiders thrown in for good measure.
* RushBoss: Like his weaker counterpart, he has low health. Unlike his weaker counterpart, he can overwhelm you with flies if he has the chance.

!!The Hollow
[[quoteright:123:https://static.tvtropes.org/pmwiki/pub/images/thehollow.png]]
->Debut: ''Wrath of the Lamb''
* BackFromTheDead: Larry Jr. devoid of blood and with swollen eyes.
* MoneySpider: The gold champion variant, which drops coins when its segments are destroyed.
* PowerFloats: The Hollow is capable of flying... somehow.
* SegmentedSerpent: As with Larry Jr., The Hollow's body segments can be destroyed separately and can cause it to split into multiple individuals.

!!The Wretched
[[quoteright:192:https://static.tvtropes.org/pmwiki/pub/images/thewretched.png]]
->Debut: ''Wrath of the Lamb''
* BackFromTheDead: Widow, drenched in blood and with her top mouth sewn shut and a more spider-like mouth in the "top" of the skull.
* BodyHorror: More so than Widow.
* GiantSpider: Like her alive counterpart.
* NoNameGiven: Until version 1.2.

!!Dark One
[[quoteright:129:https://static.tvtropes.org/pmwiki/pub/images/thedarkone.png]]
->Debut: ''Rebirth''
* BlackoutBasement: One of his attacks is to make the entire screen dark and hide in the shadows.
* BullfightBoss: He has a charge attack where he travels from one side of the screen to the other towards the player, similar to the charge attacks of Famine and War but harder to dodge.
* DarkIsEvil: Obviously.
* DegradedBoss: In [[spoiler:Sheol]].
* FrickinLaserBeams: Will shoot Brimstone straight down if you stand below him.
* OffscreenTeleportation: He can dash past the edges of the screen like the Harbingers.

!!Mega Fatty
[[quoteright:109:https://static.tvtropes.org/pmwiki/pub/images/megafatty.png]]
->Debut: ''Rebirth''
* {{Acrofatic}}: Normally slow and fat, but it has a leap attack which is executed in under a second.
* AmbiguouslyHuman: Like Peep, he's mostly human-looking, but is impossibly obese, bleeding from the mouth and eyes, and has superhuman abilities such as [[InASingleBound leaping into the sky]].
* DamageSpongeBoss: Noticeably soaks up more punishment than most normal bosses.
* DungFu: His fart attack can either produce Dips or send out a large wave of poop similar to his vomit attack.
* FatBastard: Obviously, as he's the KingMook to the Fatty class of enemies.
* {{Gasshole}}: Like normal Fatties, he has a fart attack, but it shoots out ''feces''.
* HoistByHisOwnPetard: If you have a power-up that causes tears to suspend in the air (such as Pop!), Mega Fatty's vacuum attack will suck in those tears, dealing massive damage to himself.
* KingMook: Of the regular Fatty enemy.
* VacuumMouth: One of his attacks is to suck everything in the room toward him, mimicking the effect of the item Magneto.
* VomitIndiscretionShot[=/=]WaterfallPuke: After the vacuum attack, he vomits up a barrage of projectiles that cover a portion of the screen.

!!Mega Maw
[[quoteright:131:https://static.tvtropes.org/pmwiki/pub/images/megamaw.png]]
->Debut: ''Rebirth''
* BulletHell: Its purple fire attacks are reminiscent of basic BulletHell circular attacks. There's also his red champion version where his attacks are nothing but rapid sprays of blood bullets.
* KingMook: He is a giant version of the Maws.
* MookMaker: Will spit out Hoppers occasionally.
* NonIndicativeName: Despite being called "Mega ''Maw''", he looks and behaves more like a Horf.
* PlayingWithFire: One of his attacks is to shoot flames in a circle around him.
* StationaryBoss: It always stays at the top center of the screen, no matter what.

!!Polycephalus
[[quoteright:144:https://static.tvtropes.org/pmwiki/pub/images/polycephalus.png]]
->Debut: ''Rebirth''
* BodyHorror: A cluster of eyeless, screaming heads on one body.
* ExactlyWhatItSaysOnTheTin: [[http://en.wikipedia.org/wiki/Polycephaly Polycephaly]] is the condition of having more than one head.
* GetBackHereBoss: Goes underground often, popping out only to attack.
* GlassCannon: It has lower health than most bosses, but makes up for this by staying underground until it's right in front of you, making its shots harder to dodge.
* MookMaker: Rarely spawns a Round Worm.
* NightmareFace: This boss has a perpetual one.

!!The Stain
[[quoteright:164:https://static.tvtropes.org/pmwiki/pub/images/thestain.png]]
->Debut: ''Afterbirth''
* BackFromTheDead: Polycephalus reduced to skulls conjoined with bits of connective tissue, all on top of a mound of flesh. Strangely enough, The Stain can be found on the same floor as his living version (similar to the Blighted Ovum above).
* BodyHorror: Even more-so than Polycephalus. What is left of it has now become a mound of viscera and skeleton.
* BulletHell: Fires a barrage of bullets in all directions around itself, often several times in succession.
* CombatTentacles: Has a pair of exposed blood vessels poking out from its sides, which it uses as such.
* FlunkyBoss: Occasionally spawns a pair of Chargers. The Champion version instead summons Round Worms.
* NightmareFace: Not that it wasn't already nightmarish to begin with, but when it unleashes its bullet hell attack, it opens a mouth really wide and distorts its body.

!!The Frail
[[quoteright:149:https://static.tvtropes.org/pmwiki/pub/images/thefrail.png]]
->Debut: ''Afterbirth''
* ArtisticLicenseBiology: Tapeworms don't normally have skeletons. Of course, this makes about as much sense as anything else in the game.
* BackFromTheDead: Pin has been reduced to a rotting undead corpse. And once you kill ''that'', you have to deal with DemBones.
* GlowingEyesOfDoom: While charging and firing its Brimstone beam in its second form.
* RushBoss: Even with multiple health bars, the Frail goes down quickly, but once he enters his second form, he can deal quite a bit of damage with his split shots and Brimstone lasers.
* SequentialBoss: One of the few bosses in the game with multiple health bars, and the only one that isn't a FinalBoss.
* TookALevelInBadass: In life, Pin was one of the easiest bosses in the game. As the Frail, it's surprisingly tough.
* TurnsRed: Once its health is depleted the first time, it instantly undergoes an AdrenalineMakeover, gains a new health bar, becomes faster, more aggressive, and gains several Brimstone attacks. Its black champion version skips the first phase and starts in skeletal form.
* WhatHappenedToTheMouse: Most of the original bosses got undead versions back in ''Wrath of the Lamb''... except Pin. The Frail didn't show up until ''Afterbirth''.

!!The Forsaken
[[quoteright:171:https://static.tvtropes.org/pmwiki/pub/images/theforsaken.png]]
-> Debut: ''Afterbirth''
* BackFromTheDead: Technically, the Haunt already ''was'' dead, being a ghost and all. So whatever state you put him in when you won his boss battle, he's back from it.
* TheCoatsAreOff: The Haunt has taken off his cloak/skin/ectoplasm/whatever, showing his full skeletal form instead of only his skull.
* DemBones: Ever wanted to know what a BedsheetGhost's skeleton looked like?
* FlunkyBoss: Spawns Bonies during the fight, and just like his previous incarnation, he'll go intangible if he has any minions to fight in his place.
* FrickinLaserBeams: Can fire Brimstone beams in three directions, and he can rotate the beams. Before doing this, he will always turn intangible and run away from you, so make sure you herd him towards the middle of the room, or else this attack may be impossible to dodge.
* GlowingEyesOfDoom: While firing his Brimstone attack.
* {{Intangibility}}: Will use this to flee from you so that he can fire his Brimstone attack.

!!Rag Mega
[[quoteright:192:https://static.tvtropes.org/pmwiki/pub/images/boss_rag_mega.png]]
-->Debut: ''Afterbirth†''
* CompositeCharacter: He's a combination of The Duke of Flies and Rag Man, with a bit of The Haunt thrown in for good measure.
* DetachmentCombat: His orbitals will break off and attempt to chase you when his health gets low.
* FrickinLaserBeams: Fires 3 purple beams from his orbitals.
* GlassCannon: He has relatively low health, but his orbitals block shots and can hurt you, he can shield himself inside his rags, and he has a projectile version of Rag Man's resurrection move. You'll spend most of the fight just trying to land a hit.
* MookMaker: Spawns Rag Man's Raglings throughout the fight.

!!Big Horn
[[quoteright:192:https://static.tvtropes.org/pmwiki/pub/images/boss_big_horn.png]]
--> Debut: ''Afterbirth†''
* DamageSpongeBoss: Not as tanky as Mega Fatty, but still on the high end. His constant teleporting doesn't help.
* DegradedBoss: Can summon a significantly weaker version of Little Horn during the fight.
* FeedItABomb: When his mouth opens, you can kick a bomb into it. This will stun him for a bit and cause him to take 20% more damage.
* FlunkyBoss: Occasionally summons Little Horn, though thankfully [[DegradedBoss he doesn't have nearly as much health as he did as a stand-alone boss.]]
* GetBackHereBoss: Ducks underground constantly, then reappears somewhere else in the room.
* PortableHole: He creates two or three holes around the room as his main attack, which either expands to become pitfalls or his hands will stick out and either throw bombs or chase the player. His whole body is also sticking out of one.
* ThrowDownTheBomblet: One of his attacks has him throw several bombs at the player. These can be a few troll bombs, a hot bomb, or even a mega troll bomb.

[[/folder]]

[[folder:Depths, Necropolis, Dank Depths]]

!!Loki
[[quoteright:100:https://static.tvtropes.org/pmwiki/pub/images/loki.png]]
->Debut: ''The Binding of Isaac''
* BigRedDevil: Has the stereotypical red devil appearance, although he appears to be smaller than other bosses.
* HoistByHisOwnPetard: If you can kill his Boom Flies as soon as they spawn, they will blow up on ''him''.
* FlunkyBoss: Summons Boom Flies periodically.
* HeelFaceTurn: The Little Loki item gives you a friendly Loki who uses its four-way-bullet attack. It isn't dropped by the Loki boss, though.
* TacticalSuicideBoss: The Boom Flies it spawns will often explode on him, given how powerful you should be by the time you fight him.
* TeleportSpam: Frequently teleports away during the battle.

!!Monstro II
[[quoteright:170:https://static.tvtropes.org/pmwiki/pub/images/monstroii.png]]
->Debut: ''The Binding of Isaac''
* AIBreaker: In the original game, Monstro II could be locked into his Brimstone attack by standing beside him to trigger the attack, then moving to his other side to make him shoot Brimstone in the other direction, and repeating the process as necessary. It's no longer possible with his ''Rebirth'' incarnation.
* BackFromTheDead: He is the zombified husk of Monstro.
* BodyHorror: He's three-fourths skeleton, and the one-fourth of him left isn't looking much better.
* DamageSpongeBoss: Much bulkier than the other Depths bosses.
* DegradedBoss: In [[spoiler:Sheol]] and [[spoiler:the Cathedral]].
* FlunkyBoss: Summons Suckers on his second jump attack.
* FrickinLaserBeams: Replaces his shower of bloody tears with a Brimstone attack. He'll only fire it if you're standing directly to his left or right, though.

!!Gish
[[quoteright:145:https://static.tvtropes.org/pmwiki/pub/images/gish.png]]
->Debut: ''The Binding of Isaac''
* BlobMonster: A giant tar blob.
* BonusBoss: After being unlocked, Gish will occasionally replace Monstro II.
* TheCameo: From a game with the same name, ''VideoGame/{{Gish}}''.
* FlunkyBoss: Spawns Clots.
* HeelFaceTurn: The Little Gish item gives you a friendly version with slowing attacks, and is usually dropped by the boss.
* KingMook: To the Clots.
* UndergroundMonkey: He can shoot in any direction like Monstro, summons mooks like Monstro II, and has his own unique explosive shots.

!!Mask of Infamy
[[quoteright:153:https://static.tvtropes.org/pmwiki/pub/images/maskofinfamy.png]]
->Debut: ''Wrath of the Lamb''
* AttackItsWeakPoint: The mask is invincible until you destroy her heart. Even after that, you need to hit her from behind.
* CatAndMouseBoss: The first phase of the fight: you chase the heart, while the mask chases you.
* ChasingYourTail: The second phase of the fight has you trying to attack the mask's vulnerable rear, while she continues to try and run you down.
* InterfaceScrew: The only boss without a health bar in the original version, though fixed in ''Rebirth''. The fact that it's not easy to land a shot in the last stage makes the fight look depressingly long.
* ''[[KingMook Queen]]'' [[KingMook Mook]]: A beefed-up version of the Mask + Heart enemies also added in ''Wrath of the Lamb''. Her second phase behaves much like a faster version of the Knight enemies.
* SamusIsAGirl: Confirmed to be female by WordOfGod.
* ShoutOut: Inspired by Carmillia's mask in ''Franchise/{{Castlevania}}''.
* TearsOfBlood: Bleeds from her eye sockets in a manner that makes it look like she's crying.
* WhiteMaskOfDoom: She IS one.

!!The Bloat
[[quoteright:130:https://static.tvtropes.org/pmwiki/pub/images/thebloat.png]]
->Debut: ''Wrath of the Lamb''
* AscendedMeme: His infamous reputation as a hated boss by the community is reflected in ''Afterbirth+'' challenge Aprils Fool, where he's the boss on ''every floor''.
* BackFromTheDead: What remains of Peep's bones are broken, and his eyes are swollen.
* BodyHorror: A blobby, rotting, bleeding pile of flesh with disembodied eyes that float right next to him.
* CombatPragmatist: Since he fires his Brimstone lasers the moment you're to his side or in front, chances are he may well attack you ''the instant the battle starts''.
* DeadWeight: He's a zombified version of the already obese Peep.
* DetachmentCombat: Like Peep, except both his eyes are now detached from the beginning of the fight.
* EyeScream: His eyes are covered in red growths, and aren't attached to him.
* FatBastard: Infamously morso than his alive version.
* FrickinLaserBeams: He'll fire dual Brimstone lasers from his eye sockets if you so much as put a toe in front of or beside him. This is one boss you'll ''always'' want to attack from the back, even more so than Mask of Infamy.
* MeaningfulName: "Bloat" is the medical term for abdominal distention, and he is a FatBastard. Could also be attributed to the fact that he's the rotting corpse of Peep (i.e. "bloated corpse").

!!Carrion Queen
[[quoteright:173:https://static.tvtropes.org/pmwiki/pub/images/carrionqueen.png]]
->Debut: ''Wrath of the Lamb''
* AttackItsWeakPoint: Can only be hit from behind, except when exploiting its ''other'' weak point (see FeedItABomb below).
* BackFromTheDead: A mostly-skeletal Chub.
* DungFu: Randomly produces Red Poop that damages you if you touch it and always regenerates when it's destroyed. Also can bounce off the poop as if it's a wall.
* FeedItABomb: Same as Chub, though it becomes impossible once she starts moving diagonally as she no longer charges with her mouth open.
* TurnsRed: Will bounce aimlessly around the room once her health is down to half.

!!The Adversary
[[quoteright:141:https://static.tvtropes.org/pmwiki/pub/images/theadversary.png]]
->Debut: ''Rebirth''
* BackFromTheDead: He is the posthumous version of the Dark One, covered in bandages and with a shattered horn.
* BlackoutBasement: Can turn the screen dark for his attacks.
* DishingOutDirt: He can jump up in the air and slam down, creating a circular wave of rocks around him.
* FlunkyBoss: Occasionally spawns spiders from [[TorsoWithAView the hole in his chest]].
* FrickinLaserBeams: He can now shoot Brimstone in any cardinal direction, but don't think you're safe if you stand at a diagonal, because it curves towards you.
* SillinessSwitch: Compared to the other posthumous bosses, the Adversary is pretty goofy. The only comparable one is Lokii, and he at least comes from an already cartoony boss. And yes, the dark and edgy name only makes him funnier.

!!The Cage
[[quoteright:156:https://static.tvtropes.org/pmwiki/pub/images/thecage.png]]
->Debut: ''Rebirth''
* BackFromTheDead: He is a posthumous version of Mega Fatty, with his head being absent (assuming it got chopped off) and his body rotting, along with a new stitch across his stomach, making him resemble a giant Vis.
* DamageSpongeBoss: Notably, he has more health than ''Mom''.
* DeadWeight: It's the zombified version of [[FatBastard Mega Fatty]], so naturally he is mobidly obese.
* DishingOutDirt: His jumping attack now creates sharp rocks like the Adversary's, but he creates lines of them that travel outwards in several directions until they hit a wall.
* DualBoss: The pink Champion variant pits the player against two Cages.
* GiantMook: He's basically been turned into a Vis, making him this.
* MookMaker: He can spawn discoloured Vis that fire sickly grey Brimstone lasers.
* RollingAttack: He can curl up in a ball and roll around the floor in an attempt to hit Isaac.
* ZombiePukeAttack: It manages to do this without a ''head''.

!!The Gate
[[quoteright:168:https://static.tvtropes.org/pmwiki/pub/images/thegate.png]]
->Debut: ''Rebirth''
* BackFromTheDead: He is a posthumous Mega Maw, as the flesh from his face leaks to the lower half of his head, his skull remains animated for the time it's alive.
* FlunkyBoss: Spawns a series of Leapers in order to set up his Brimstone attack.
* MeatPuppet: A pair of eyes can be seen whenever The Gate opens his mouth. When defeated, something that looks like a tiny Isaac peeks outside a crack right before expiring.
* ReflectingLaser: One of his attacks is to spawn three Leapers and then fire a Brimstone laser that connects between the three and deals a whole heart of damage. Killing the Leapers before he fires it causes the beam to simply travel straight down instead. Interestingly, the effect isn't just limited to Leapers - if the Gate spawns with other enemies (e.g. Greed Mode and Boss Rush), the laser chains to those enemies as well and will most likely kill them for you.
* StationaryBoss: Just like its living counterpart.

!!Brownie
[[quoteright:152:https://static.tvtropes.org/pmwiki/pub/images/brownie.png]]
->Debut: ''Afterbirth''
* AbnormalAmmo: Corn.
* BulletHell: Tends to fire much larger volleys of projectiles than most bosses. Also drops Corn Mines that explode into even more projectiles.
* FlunkyBoss: Spawns Brownie Corns in large numbers throughout the fight.
* OneHitKill: Using Flush! will instantly kill him and any Brownie Corns, without him turning into Dangle.
* RushBoss: Although its attacks and minions can be difficult to dodge, Brownie doesn't have a particularly large health pool. The fact that one of its attacks is essentially CastFromHitPoints doesn't help its case.
* TacticalSuicideBoss: The exploding turds Brownie places down can not only damage it, they can also ''poison'' it. Zig-zagged in that Brownie also trails poisonous creep while poisoned.
* ToiletHumor: How else does one describe a giant ball of poo that shoots corn?
* TurnsRed: Inverted. When its health drops low, it turns into Dangle.

!!Sisters Vis
[[quoteright:192:https://static.tvtropes.org/pmwiki/pub/images/boss_sisters_vis.png]]
->Debut: ''Afterbirth†''
* TheCameo: Originally appeared as bosses in Edmund's earlier game, ''Gish''.
* DistaffCounterpart: To The Cage. They're female and look almost identical to him, except they have heads. They were also supposed to debut in Afterbirth, but were cut and replaced with the pink Champion Cage (which is, of course, two Cages).
* DualBoss: Sisters Vis spawns in pairs by default. Can come in as many as eight at once in Greedier Mode.
* GiantMook: A pair of giant Vis, although they don't really look like them.
* RollingAttack: Just like The Cage.
* TurnsRed: When one Sister is killed, the other will literally turn red and begin moving faster.
* WaveMotionGun: Much like the Vis enemies, their main attack is opening up their stomach and firing blood lasers, although their's is much larger than normal. They usually do it facing towards each other, but if one does it alone (or the other one is dead), they will sweep it left to right.

[[/folder]]

[[folder:Womb, Utero, Scarred Womb]]

!!Blastocyst
[[quoteright:120:https://static.tvtropes.org/pmwiki/pub/images/blastocyst.png]]
->Debut: ''The Binding of Isaac''
* AsteroidsMonster: As it gets damaged, it splits into smaller blobs. The smallest blob variety leaves behind the Embryo inside when destroyed.
* BlobMonster: Judging by the name, it's a gigantic, blob-like cell.
* BulletHell: Can happen if too many of them are left onscreen. Since they only fire in a set direction, however, it's pretty tame compared to most other examples in the game.
* FakeUltimateMook: Amusingly enough, the helpless Embryos that spawn as regular enemies on early floors had mini-boss health bars in the original game, as the game counted them as Blastocyst.
* KingMook: To the Embryos found in early stages.
* MegaMicrobes: They're cells/developing embryos that are bigger than Isaac.
* WeaksauceWeakness: Poison. Normally a boss would only take a bit of damage from poison as their health bars reach in the hundreds but if Blastocyst is poisoned when it divides it's instantly killed, ending a long boss fight with in a few minutes.

!!Scolex
[[quoteright:132:https://static.tvtropes.org/pmwiki/pub/images/scolex.png]]
->Debut: ''The Binding of Isaac''
* AttackItsWeakPoint: You can only damage it by hitting it in the very back segment.
* FragileSpeedster: It has the lowest health of any boss in the game, but it makes up for this with its speed and hard to hit weakpoint. ''Rebirth'' gave Scolex a health buff, but it still takes less damage than every other Womb boss.
* TacticalSuicideBoss: One of its attacks has it poking its vulnerable tail out of the ground for a fairly lengthy period of time before firing three Ipecac shots, giving the player a perfect opportunity to take off a lot of its health.
* UndergroundMonkey: It's a much tougher version of Pin, but unlike the BackFromTheDead versions of other bosses, Scolex is noticeably different in appearance from its easier version (and was also in the game ''before'' Pin).

!!Daddy Long Legs
[[quoteright:117:https://static.tvtropes.org/pmwiki/pub/images/daddylonglegs.png]]
->Debut: ''Wrath of the Lamb''
* EasterEgg: There is an item that summons the Daddy Long Legs to stomp enemies in an area the player is standing in without hurting them. Using this against the Daddy Long Legs reskins it as the Triachnid's claw. Using it against Triachnid, however, flat-out doesn't work.
* GiantFootOfStomping: Yes, this game has a spider that stomps ''you''. No, it (most likely) does not take place in [[RussianReversal Soviet Russia]].
* GiantSpider: Bigger than any other spider in the game, taking up more than the screen can show.
* HeelFaceTurn: The Daddy Long Legs item makes him periodically stomp on your enemies for you.
* KingMook: A giant spider, same as Widow.

!!Triachnid
[[quoteright:104:https://static.tvtropes.org/pmwiki/pub/images/triachnid.png]]
->Debut: ''Wrath of the Lamb''
* TheCameo: Triachnid is a reference to a previous flash game by Edmund [=McMillen=]. Furthermore, Triachnid is an alternate of Daddy Long Legs; in his own game, Triachnid was finding a home for his young.
* DummiedOut: [[http://edmundm.com/post/24457249299/isaac-expansion-expansion As hinted here]], Triachnid was originally cut before the game was released. It wasn't removed ''entirely'', though. Due to a glitch, it originally would replace [[spoiler:the Cathedral's TrueFinalBoss.]] This was eventually corrected, and Triachnid was added in as a normal boss.
* GiantFootOfStomping: Shares Daddy Long Legs' stomp attacks, but while Daddy Long Legs has four legs to stomp you with, Triachnid only has three.
* UndergroundMonkey: Occasionally replaces Daddy Long Legs once unlocked.

!!Lokii
[[quoteright:133:https://static.tvtropes.org/pmwiki/pub/images/lokii.png]]
->Debut: ''Wrath of the Lamb''
* TheArtifact: With the "Double Trouble" mechanic in ''Rebirth'', Lokii is kind of redundant; the fact that the halves summon Red Boom Flies instead of regular Boom Flies is the only way they're different from a Double Trouble Loki fight, aside from appearing in standard 1x1 boss rooms.
* BackFromTheDead: Loki has been split in two, but both halves live on.
* DualBoss: He's the equivalent of fighting two Lokis at once, only with Red Boom Flies.
* FlunkyBoss: Unlike standard Loki, they summon ''Red'' Boom Flies. This gives them an advantage because they won't be blasted in the face if their minions die near them.
* HalfTheManHeUsedToBe: They're Loki after being split in half, and somehow they're completely fine.
* TeleportSpam: Just like normal Loki.
* VisualPun: The last two "i"s of his name have a line crossed through them on the bottom, making them resemble part of the Roman numeral II.

!!Teratoma
[[quoteright:129:https://static.tvtropes.org/pmwiki/pub/images/teratoma.png]]
->Debut: ''Wrath of the Lamb''
* AsteroidsMonster: The same as Fistula, except now filled with spiders instead of Chargers. The biggest difference between them is that Teratoma's largest form splits into three, whereas Fistula splits into four.
* BackFromTheDead: Kind of. It's the posthumous version of Fistula in mechanics, although given that both are different real-life tumors without any personality or even attack method, it's hard to to say how "posthumous" they can really be.
* BodyHorror: Like Fistula, it's named after a real-life phenomenon in which the body forms a growth containing all three germ layers, one of which can potentially manifest as ''bone shards and teeth!''

!!Mama Gurdy
[[quoteright:162:https://static.tvtropes.org/pmwiki/pub/images/mamagurdy.png]]
->Debut: ''Rebirth''
* AscendedMeme: Apparently a reference to a fan-made animation.
* EmergingFromTheShadows: The boss screen shows her arm doing this. She actually looks like [[https://gamepedia.cursecdn.com/bindingofisaacre_gamepedia/0/0b/Mama_Gurdy_ingame.png?version=5286da1454db10196c163c99cd17983b this]] in-game.
* {{Metamorphosis}}: The fourth form of Gurdy to appear. This one is quite different than her predecessors - instead of a ball of guts with a human face, it's a (probably) humanoid creature that's misshapen and lumpy.
* SpikesOfDoom: She is able to create spikes around the room.
* WallMaster: She can hide in the walls of the boss room, immune to damage.
* WeaksauceWeakness: She never creates spikes directly under the player, so standing still during her spike attack will leave you safe and her defenseless.
* ZombiePukeAttack: One of her moves has her spew orange vomit all over.

!!Mr. Fred
[[quoteright:135:https://static.tvtropes.org/pmwiki/pub/images/mrfred20.png]]
->Debut: ''Rebirth''
* FlunkyBoss: Starts the fight accompanied by four Homunculi whose bonds he can break at will, and spawns Freds throughout the fight.
* KingMook: A giant boss version of the enemy Fred that appears in Chapter Four.
* StationaryBoss: Never moves from the centre of the room.

!!The Matriarch
[[quoteright:192:https://static.tvtropes.org/pmwiki/pub/images/boss_the_matriarch_2.png]]
->Debut: ''Afterbirth†''
* BodyHorror: She is a giant maggot wrapped in a chunk of rotting flesh also infested with a bunch of smaller maggots. Is there any more to be said?
* CompositeCharacter: She's Chub [[EquippableAlly wrapped up]] in a Fistula, although the boss doesn't actually take any attack patterns from those two.
* FeedItABomb: On second thought, ''[[DefiedTrope don't]]''. Unlike regular Chub, the Chub that spawns when the Matriarch takes enough damage will spit the bomb back at you.
* KingMook: She is to the Fistuloid enemies what Chub is to the Chargers.
* TookALevelInBadass: The boss ''is'' Chub character-wise (she turns in to Chub after losing all her health as the Matriarch), but now clad in a Fistula mass of flesh and fought much later in the game.
* TurnsRed: After being damaged enough, the Matriarch fires a wave of Fistulas that quickly break into maggots, and can do this attack at any time after that point.

[[/folder]]

[[folder:Shared]]
!!The Fallen
[[quoteright:133:https://static.tvtropes.org/pmwiki/pub/images/thefallen.png]]
->Debut: ''The Binding of Isaac''
* AsteroidsMonster: After about 75% of his health his gone, he splits into two versions of himself.
* BullfightBoss: Does this when he isn't shooting. The charge is stopped by shooting him enough times or when he reaches you, after which he'll [[BeamSpam shoot blood in every direction.]]
* ClassicVideoGameScrewYou: It's uncommon, but this guy can be the boss of ''any'' dungeon save ones with predetermined bosses. He's notorious for showing up in the Basement/Cellar, often before you've had a chance to buff your speed and survive his charge.
** Somewhat downplayed since he gives you a free devil room item [[note]]And that includes the likes of Brimstone and The Pact[[/note]] if you manage to beat him. Because of this, veteran players may actually be happy to find him early on in a run.
* DegradedBoss: In [[spoiler:Sheol. He's later fought at full strength when the Satan fight begins.]]
* EarlyBirdBoss: He can replace ''any'' boss that's not pre-set by the level. If you're unlucky, he can appear on the first or second floor.
* TheDragon: To [[spoiler:Satan]]. He even acts as the first stage of his master's boss fight!
* HighPressureBlood: He shoots Brimstone lasers in all four cardinal directions at once for one of his attacks.
* {{Nerf}}: In ''Rebirth'', The Fallen's health scaling scales based on the floor, making him significantly weaker on early floors. Additionally, he now only appears if you've been inside a Devil Room previously.

!!Krampus
[[quoteright:219:https://static.tvtropes.org/pmwiki/pub/images/krampus23.png]]
->Debut: ''Wrath of the Lamb''
* BadSanta: Drops a Lump of Coal.
* ChestMonster: Randomly appears in Devil Rooms. He's more likely to appear if you have already entered a Devil room, even more so if you've made a deal.
* ClassicVideoGameScrewYou: Krampus can appear in the first Devil Room, potentially invalidating any chance to see further Devil Rooms merely by being there. Also, just by showing up, he invalidates a hard-earned devil deal in favor of an item that may or may not help as much as the stuff you were hoping for... assuming he doesn't just kill you, that is. It doesn't help that Krampus gets buffed with every major update to the game.
** At least partially subverted if you're targeting Mega Satan. Getting a Krampus item doesn't ruin your chances for Angel rooms in later floors, therefore making it easier to get the Key Pieces.
* EarlyBirdCameo: He can be fought in Greed mode, even if he hasn't been unlocked yet.
* HighPressureBlood: Just like the Fallen, but he'll do it if you pass by him in any direction rather than after a charge. ''Afterbirth'' adds in a chance of him rotating his beams, and ''Afterbirth+'' adds in a chance of him firing them off ''diagonally''.
* TheKrampus: It's in the name, after all.
* MiniBoss: By virtue of being a weaker version of the Fallen, not to mention he has the same kind of entrance as the Seven Deadly Sins. Though unlike the Sins, he only appears in Devil Rooms and is the only mini-boss that [[AllYourPowersCombined Delirium]] can turn into.
* PaletteSwap: Of The Fallen, except he doesn't split into two parts and is mildly weaker. He also has no charge attack [[note]]Though an update in ''Afterbirth+'' gave him a quick lunge attack[[/note]], firing off his Brimstone lasers if you stick to any cardinal direction of him for too long instead. He can also fire them diagonally and rotate them around the room. Killing him may drop the Head of Krampus, which lets you use this attack.

!!Uriel and Gabriel
[[quoteright:181:https://static.tvtropes.org/pmwiki/pub/images/urielgabriel.png]]
->Debut: ''Rebirth''
Secret bosses in ''Rebirth'', a fight with one of two Angels is initiated by bombing the statue in an angel room at any point throughout the game. Beating one unlocks a piece of a key each time, and beating both and combining the keys allows the player to unlock the true final boss of the game.

* TheBlank: Even when not in statue form, they lack faces.
* BoltOfDivineRetribution: They shoot coherent beams of holy light, which functionally behave like Brimstone lasers.
* ColorCodedForYourConvenience: Uriel wears silver or blue, Gabriel wears red.
* DegradedBoss: Two [[spoiler:Fallen Angels]] attack you as [[spoiler:Mega Satan's flunkies]], and to get to that point you're almost required to have already killed the normal ones in this run. [[spoiler:One interpretation of this is that they kept the pieces of the Golden Key safe, failed when Isaac took the pieces and were subsequently punished for it.]] Incidentally, the degraded versions are actually ''stronger'' than the originals.
* DismantledMacGuffin: They each hold a piece of the key required to open the Gold Gate.
* DualBoss: ''Afterbirth+'' gave Angel Rooms a chance to contain two angel statues, letting you fight both at once if you are so inclined (or are short on bombs, or used Mama Mega on the same floor). However, fighting both at once will only spawn one Key Piece, making it better to fight them in sequence.
* EarlyBirdBoss: Though Gabriel is the stronger of the two, they spawn in random order, making it possible to fight him rather than Uriel on an early floor.
* GuideDangIt: [[spoiler:Bomb the angel statue in an Angel Room to provoke it into a fight. Less aggravating than other examples since there are more in-game clues and it is often next to blue fires, which can be bombed for soul hearts, so the player might figure this out by mistake if nothing else.]]
* HiddenInPlainSight: [[spoiler:Those statues in the Angel Room aren't just there for decoration. A fight can be initiated at any point in the game, provided you have beaten either ??? or The Lamb and a spare bomb.]]
* OurAngelsAreDifferent: They are much larger than Isaac and have [[TheBlank no faces]]. They're also [[LightIsNotGood hostile and attack Isaac]] like every other boss in the game.
* PaletteSwap: Their main distinction is the color of their scarves. Uriel wears a pale blue one, while Gabriel's is red.
* PersonalSpaceInvader: Unlike Uriel, Gabriel likes to fly directly at Isaac to deal contact damage.
* WingedHumanoid: Albeit [[TheBlank without a face]].

[[/folder]]

[[folder:The Harbingers]]

!!!In General

The four HorsemenOfTheApocalypse, unlocked after beating Mom for the first time. Famine, Pestilence, War, and Death each have the ability of replacing one of the bosses of the Basement, Caves, Depths, and [[spoiler:Womb]] respectively, while the Headless Horseman has the capability to replace any of these bosses, and Conquest was introduced as an alternate boss to Death.
----
* CombatBreakdown: Interestingly, most of the Horsemen actually get ''easier'' in their second phases, usually due to you destroying parts of them. The main exceptions are Famine, who switches to a SpreadShot that isn't much easier to dodge than his charge and Pooters, and Conquest, who never changes behavior.
** Pestilence is reduced to spitting Attack Flies after losing his head, whereas his first phase spawns Chargers.
** War loses all of his existing attacks after his horse is destroyed, at which point all he does is run at you.
** After jumping off his horse, Death's only attack is to spawn Knights which, more often than not, get run over by said horse. The horse itself also follows a much more predictable pattern than his first phase's scythes and Hourglass.
* DegradedBoss: In later stages.
* HorsemenOfTheApocalypse: The very same ([[TheLastOfTheseIsNotLikeTheOthers except the Headless Horseman]]). Like many portrayals, Pestilence initially took Conquest's place before Conquest himself was added.
* OffscreenTeleportation: Most of them charge against you through the screen and return from the other side.
* QuirkyMinibossSquad: Despite being full bosses in their own right and fought one at a time, they still fit the bill. Their item drops, the Cube of Meat and the Ball of Bandages, become more powerful by collecting more Cubes or Balls from multiple Horsemen, they can be summoned by the Book of Revelations, multiple Horsemen will appear at the same time as normal enemies in later levels, and they're easily recognizable.
* SequentialBoss: With two stages. Except for Conquest and the Headless Horseman, the latter being a DualBoss.
* SignatureRoar: The Horsemen that charge at you let out a distinctive shout before doing so.
* UncattyResemblance: Each of the Horsemen's horses look similar to their rider.

!!!Famine
[[quoteright:100:https://static.tvtropes.org/pmwiki/pub/images/famine.png]]
->Debut: ''The Binding of Isaac''
* BodyHorror: EyelessFace and physical degradation in general. The lack of lips is especially noticeable.
* LosingYourHead: After taking enough damage, Famine's body explodes, leaving only his floating head.
* MookMaker: Creates Pooters.
* SlasherSmile: Famine has this as his trademark.
* WarmUpBoss: As the Horseman of the Basement, Famine has the lowest health and simplest attack pattern out of the Harbingers.

!!!Pestilence
[[quoteright:138:https://static.tvtropes.org/pmwiki/pub/images/boi_pestilence_5.png]]
->Debut: ''The Binding of Isaac''
* BodyHorror: No eyes, rotting body with swollen parts, filled with explosive, possibly-toxic fluids, and surrounded by maggots and flies.
* GreenAroundTheGills: His ''entire body'' is sickly green, swollen, and leaking some sort of disease-ridden fluid. So is his horse.
* IncurableCoughOfDeath: His hoarse coughs summon flies.
* LosingYourHead: Only the body (still riding the horse) remains after the first part.
* MookMaker: Maggots at first, Flies later.
* WalkingWasteland: As the personification of disease and toxin, he leaves a trail of creep everywhere he moves.

!!!War
[[quoteright:140:https://static.tvtropes.org/pmwiki/pub/images/war.png]]
->Debut: ''The Binding of Isaac''
* BullfightBoss: After losing his horse.
* BullSeeingRed: He's red, and his horse has bull horns and charges.
* MadBomber: One of his attacks drops bombs randomly.
* OhCrap: After losing his horse, hit him enough times and he'll fall to the ground stunned, with a terrified look on his face.

!!!Death
[[quoteright:158:https://static.tvtropes.org/pmwiki/pub/images/death.png]]
->Debut: ''The Binding of Isaac''
* DeathsHourglass: A literal example, in that one of his first stage's attacks is to use the Hourglass item on Isaac.
* DualBoss: He hops off his ride on his second stage, which goes on ramming aimlessly while he hovers around spawning Knights.
* TheGrimReaper: The skeletal kind, complete with black cloak and scythes.
* MookMaker: Creates Knights.
* ShoutOut: One of his attacks is very similar to one that [[Franchise/{{Castlevania}} a certain other Death]] you may know of uses.
* SinisterScythe: He can summon flying, spinning scythes to attack.
* VisualPun: His champion form is [[TheBlackDeath black]]. Reinforced by the enemies summoned by the champion version: the Red Maws summoned by the first form reference the swelling caused by the disease, while the Kamikaze Leeches refer to the use of leeches as a treatment for the blood build-up.

!!!The Headless Horseman
[[quoteright:107:https://static.tvtropes.org/pmwiki/pub/images/headlesshorseman.png]]
->Debut: ''The Binding of Isaac''
* AllYourPowersCombined: The head has Famine's triple shot and War's triple charge, while the body is Pestilence minus spawning enemies. Plus, you fight two bosses at the same time, which is what happens when Death loses half his health.
* ClassicVideoGameScrewYou: He can replace any horseman. Are you on the Womb/Utero 1, with Book of Revelations and Level 3 Meat Boy or Bandage Girl, hoping to finally get the corresponding achievement for Level 4? Too bad, have a pony instead.
* DegradedBoss: The head alone can appear in normal rooms once you reach the Depths. The body can as well starting from [[spoiler:Sheol/Cathedral]].
* DualBoss: The boss is split into: his head, that charges and shoots small bullets, and his body, which shoots large bombs and leaves trails of blood.
* EarlyBirdBoss: While the Headless Horseman is manageable with a few items, he can just as easily show up in the Basement and wipe the floor with you due to being much stronger than just about any other Basement boss.
* HeadlessHorseman: [[ShapedLikeItself Well, yeah.]]

!!!Conquest
[[quoteright:122:https://static.tvtropes.org/pmwiki/pub/images/conquest.png]]
->Debut: ''Wrath of the Lamb''
* BeCarefulWhatYouWishFor: Some players complained that War was "too easy" for a boss in the Depths.
* BoltOfDivineRetribution: One of only two bosses in the game to summon beams of light from on high.
* ClassicVideoGameScrewYou: Like the Headless Horseman, he can replace other Horsemen (although he will only replace War or Death in vanilla Isaac or just Death in ''Rebirth''), dicking players out of getting the Meat Boy/Bandage Girl achievements countless times.
* ContinuityNod[=/=]GeniusBonus: [[invoked]] The secret calls him "A Forgotten Horseman", reflecting the fact that he's been replaced by Pestilence both in the game and in nearly every other version of the HorsemenOfTheApocalypse. Also, it was replaced because it was too similar to War. Conquest has improved versions of War's attacks.
* DoppelgangerAttack: He can charge across the screen alongside five or so clones. In ''Rebirth'', it's upgraded to about a dozen.
* EyepatchOfPower: A full blindfold in his case.
* HolyHandGrenade: His beam attack.
* LightIsNotGood: As a Horseman of the Apocalypse, this is a given.
* MissingSecret[=/=]DummiedOut: Weird variation. Conquest does not need to be specifically unlocked, [[http://imgur.com/a/AZ5GE but there is an unused picture for unlocking him.]] Subverted in ''Rebirth'', where taking ten angel room items unlocks him.
* SharedLifeMeter: During Conquest's DoppelgangerAttack, hitting any of his duplicates will cause damage to the main Conquest. If his health drops to zero during this attack, all Conquests will die at the same time.
* SixthRanger: An additional horseman added later. Technically, the original passage from the Book of Revelations likely referred to Conquest, not Pestilence, but the most modern usage of the horsemen ignore Conquest.

[[/folder]]

[[folder:The Seven Deadly Sins]]
->Debut: ''The Binding of Isaac''
->Debut (Super variants and Ultra Pride): ''Wrath of the Lamb''

!!!In General
* AmbiguouslyHuman: It's not clear if they are humans under the effect of various items[[note]]The Virus makes Isaac resemble Lust without the pink coloration and Mr. Mega gives him Wrath's "mask"[[/note]], humanoid monsters from the start, or the actual Sins themselves given physical embodiment. The implication that [[spoiler:every character is an alternate Isaac as he only imagined the events of the gameplay]] just complicates things further.
* AnthropomorphicPersonification: Of their respective sins.
* DegradedBoss: Like most of the bosses, they can be found in regular rooms towards the end chapters of a run. However, they will still have specific "miniboss rooms" complete with the music and "Vs" text appearing at the top of the screen in chapter 5.
* KingMook: The "Super" variants introduced in ''Wrath of the Lamb'', as well as Ultra Greed in ''Afterbirth''.
* InescapableAmbush: Unless you hold certain items, they won't show up on the map at all until you run into them, and you cannot leave unless you carry a teleportation item. Their rooms also have metal bars around the doors so that you cannot even bomb your way out as you could with normal enemy rooms.
* QuirkyMinibossSquad: They fight you individually, but in any of the levels following the fourth chapter, you may encounter up to three different Sins to fight in the same room.

!!!Envy/Super Envy
[[quoteright:132:https://static.tvtropes.org/pmwiki/pub/images/envy.png]]
* AsteroidsMonster: When defeated, he splits into two heads, which each split into two smaller heads, which finally each split into two tiny heads. Super Envy splits into threes instead of twos, except for the smallest heads.
* DamageSpongeBoss: To make up for the fact that he is easily the least dangerous Sin in either form, he has more aggregate health than the other Sins.

!!!Gluttony/Super Gluttony
[[quoteright:142:https://static.tvtropes.org/pmwiki/pub/images/gluttony21.png]]
* DoesThisRemindYouOfAnything: if you stand above Gluttony so that he shoots upwards, it looks disturbingly like he's flashing you. Which, like Vis, he kinda is. [[BodyHorror To the viewer's]] [[BloodyMurder utter chagrin]].
* FatBastard: Par for the course for a Gluttony personification.
* HighPressureBlood: He shoots Brimstone lasers from his belly, like a Vis. Super Gluttony fires out his back, too, like a Double Vis.
* KingMook: He's basically a Vis with a head.

!!!Greed/Super Greed
[[quoteright:132:https://static.tvtropes.org/pmwiki/pub/images/greed9.png]]
* BanditMook: His shots (and [[CollisionDamage mere contact]] with him) take away a couple of pennies from you, while making you drop a variable amount on the floor that you can try to retrieve. Just be careful while doing so, if you don't want to be [[DeathByMaterialism killed in the process]]. His mook-look-alikes have the same ability as him.
* BreakoutCharacter: He's the most memorable and ubiquitous of The Seven Deadly Sins mini-bosses, and ''Wrath of the Lamb'' cemented his status by adding a quite a few new versions of him. [[spoiler: And ''Afterbirth'' makes Ultra Greed the final boss of Greed Mode.]]
* CharacterBlog: The ''Afterbirth'' AlternateRealityGame [[https://twitter.com/iamisaacsbody gave him a Twitter]]. On the other hand, most of the entries were made by the ''players'', who completed the ARG by logging into the account and posting tweets.
* ChestMonster: Replaces shops and secret rooms. He's more likely to appear as you go further in the game.
* {{Expy}}: He shares some traits with ''VideoGame/{{Spelunky}}''[='=]s Shopkeeper, including his multi-shot ability, potential to turn hostile on the player without previous warning, and overall [[{{Jerkass}} dickishness]].
* FlunkyBoss: Normal Greed summons Hoppers, Super Greed summons Keepers (which are Greed heads).
* KingMook: ''Wrath of the Lamb'' added Super Greed, who is bigger, meaner, scarier, and can spawn Keepers, who are essentially Greed heads. They can also appear in the Depths, the Catacombs, and the Necropolis. [[spoiler:Also, the final boss of ''Afterbirth''[='=]s Greed Mode is Ultra Greed.]]
* MookPromotion: {{Inverted|Trope}}. The game's standard version features him as a mini-boss, but the expansion added mook-versions of him that share some of his most aggravating attributes.[[note]]Multi-shot and, most importantly, the ability to drain your money.[[/note]]
* ShopKeeper: When he's not out for your blood, anyway.
* MoneyForNothing: {{Invoked|Trope}}; he gives a lot of money when defeated, but his battle has a tendency to replace a shop where there would ''be'' one. There's also a chance he might appear in Secret Rooms, making for a bit of a subversion.
* TookALevelInBadass: He's pretty unimpressive as a mini-boss even in his super form, then comes [[spoiler:his Ultra Greed form]].
* WingdingEyes: Super Greed either has cent signs for eyes or actual coins jammed in his eye holes.

!!!Lust/Super Lust
[[quoteright:132:https://static.tvtropes.org/pmwiki/pub/images/lust.png]]
* AbhorrentAdmirer: Possibly due to being the personification of Lust and not exactly in the [[BodyHorror good-looking department]], and her only attack is chasing after the player in great speed and causing CollisionDamage.
* BadassNormal: Pride can spawn bombs from nowhere and either has electrical powers or can stretch out tentacles. Greed can sap money away from Isaac through collision or even ''bullet contact'' and can spawn monsters. Lust, however, just seems to be a fast girl with a harmful virus. Super Lust averts this by having a trail of harmful blood that doesn't damage her, which is not "normal" by any standard.
* BloodyHorror: Lust seems to be affected with some sort of blood disease (likely HIV) and her Super variation bleeds from the face and leaves a trail of blood everywhere she goes.
* BodyHorror: Super Lust's horribly deformed face.
* BullfightBoss: She does nothing but charge at you. Thankfully, she can't turn on a dime and there are plenty of rocks around to kill her momentum.
* FragileSpeedster: Not really that tough of a battle compared to the other Deadly Sins since her only gimmick is just running really fast, and she can be brought down rather quickly even with no special tear upgrades. What would make her dangerous though is if you had a very poor speed stat.
* PinkMeansFeminine: Both Lust and her super form are pink, and she's the only Sin who is female.
* TheSmurfettePrinciple: The only one of the Sins/Super Sins that have been identified as female.

!!!Pride/Super Pride
[[quoteright:132:https://static.tvtropes.org/pmwiki/pub/images/pride.png]]
* CombatTentacles: It's either this or ShockAndAwe.
* MadBomber: Occasionally, Pride randomly spawns troll bombs in an attempt to catch you in the blast.
* PaletteSwap: In ''Wrath of the Lamb'', Super Pride's appearance was just that of Pride, but larger and pink instead of grey. In ''Rebirth'', the face is slightly different, but he still resembles a giant, pink Pride.
* ShockAndAwe: Both forms of Pride can do this.

!!!Sloth/Super Sloth
[[quoteright:132:https://static.tvtropes.org/pmwiki/pub/images/sloth11.png]]
* MadBomber: He'll belch out green spit bombs.
* MookMaker: He'll spawn Chargers on occasion.
* PaletteSwap: Of the Globin. See below.
* StealthPun: Unlike the other sins, Sloth is a PaletteSwap of an existing enemy. ''Sloth has a lazy character design.''

!!!Wrath/Super Wrath
[[quoteright:132:https://static.tvtropes.org/pmwiki/pub/images/wrath.png]]
* CartoonBomb: His bombs are identical to yours, skull marking and all.
* {{Expy}}: Of VideoGame/{{Bomberman}}.
* HoistByHisOwnPetard: Wrath's bombs can be pushed around like player-dropped bombs, allowing you to push them back towards him for a nice chunk of damage. This doesn't work on Super Wrath's troll bombs, though. Even more amusingly, any items that affect bombs will affect the bombs dropped by Wrath/Super Wrath. This can result in [[HilarityEnsues hilarious situations]] where, if you have the Bobby-Bomb collectible, every bomb the boss drops proceeds to walk back toward him.
* MadBomber: Throws bomb after bomb at you. Since he's Wrath, this doubles as a StealthPun.
* TacticalSuicideBoss: Probably the finest example in the game, as he has exactly one attack which can easily [[JustForPun blow up in his face]]. Less so with Super Wrath, as he throws Mega Troll Bombs, which follow the player around and cannot be pushed. However, these can potentially be lured into him.
* WrongGenreSavvy: He seems to think he's in a Bomberman game. Which doesn't work out too well for him since Isaac can just push his bombs back at him with tears.

!!!Ultra Pride
[[quoteright:126:https://static.tvtropes.org/pmwiki/pub/images/ultrapride.png]]
* CreatorCameo: He's a stylized representation of artist Edmund [=McMillen=], while his familiar is one for programmer Florian Himsl. Hence why he's named Ultra Pride.
* DeathByCameo: You do fight them, after all.
* DualBoss: He comes with his familiar, and both have to be defeated.
* MeaningfulName: The creators are ultra proud of their product. Additionally, putting yourself as a cameo in your own game is a flagrant show of pride.
* PaletteSwap: He's basically Sloth with different moves, while the familiar is a graphically altered Baby with a different shot type.

[[/folder]]

[[folder:Final Bosses]]

Yes, boss''es''. At first, you end the playthrough in Depths II and kill Mom, but as you beat the game repeatedly, you unlock more chapters, each with a FinalBoss bigger and tougher than before.

All spoilers are unmarked from here on out. Proceed at your own caution!

!!Mom
[[quoteright:141:https://static.tvtropes.org/pmwiki/pub/images/momleg.png]]
->Debut: ''The Binding of Isaac''
At the end of the Depths, Isaac finally confronts his mother. As her foot stomps down on Isaac from above, she looks and sends her hands through the doors of the boss room while spawning enemies. But even if Isaac defeats Mom, it's not the end.
----
* AttackOfTheFiftyFootWhatever: Her boss fight.
* AxCrazy: Her goal is to kill her own son, and she doesn't sound too upset about it during the fight, what with the laughing and all.
* BattleThemeMusic:
** The original game had "''[[https://www.youtube.com/watch?v=_q9ZC-UwViM Thine Wrath...]]''", an orchestrated theme that sounds nearly angelic at points while still being dreadful, to symbolize Mom's willingness to kill her own son to appease what she perceives as "God".
** ''Rebirth'' gave her "''[[https://www.youtube.com/watch?v=EBJEHIxHuKE Matricide]]''", which leans more to heavy rock and an oppressive tone backed up by a choir.
* BodyHorror: The way Mom's body parts move throughout the fight (such as both eyes appearing on opposite sides of the room while she tries to stomp on you) suggest an ability to contort herself in rather...impossible ways.
* BossBanter: ''ISAAAAAC!''
* DeathByIrony: Crushed by her own bible!
* DiscOneFinalBoss: Demoted to this on your second playthrough and beyond.
* EvilIsVisceral: Likely the reason her body parts are detailed and somewhat deformed.
* EvilLaugh: She lets out one every time she successfully damages Isaac.
* EvilMatriarch: A monstrous final boss in the form of Isaac's mother.
* TheFaceless: Her entire face is never shown at any point in the main game (the intro and epilogue don't count, as they're Isaac's cartoon drawings). This is [[SubvertedTrope subverted]] after you beat the Chest in ''WOTL'' or ''Rebirth'', but only briefly. In photographs, to be precise.
* FanDisservice: When Isaac uses the Mom's Bra item, a picture of his mother's shirtless torso flashes on the screen. A ''very'' unflattering picture of his mother's less-than-fit shirtless torso.
* FatBastard: As shown by her giant leg and the picture that shows up when using Mom's Bra.
* FinalBoss: In your first playthrough. She's nowhere near the TrueFinalBoss, though.
* FlunkyBoss: She'll summon groups of random enemies to battle Isaac.
* GameplayAndStoryIntegration: Using the Bible instantly defeats her in her boss fight.
* GiantFootOfStomping: Her main method of direct attack.
* {{Gonk}}: See that leg up above? That's all the proof you need.
* GrossUpCloseUp: One of her leg in the boss portrait, and one of her body in the picture that appears when using Mom's Bra.
* HumanoidAbomination: Most of what she does in-game and in a few cutscenes blatantly disregards normal body movements if not physics. She can step on her own eye, generally alter her size, and her arm can fit in a chest inside her heart inside her womb.
* MookMaker: Spawns an array of previous enemies to make her battle harder. She does it from her body fat, which almost pours out of the boss room doors.
* MotherOfAThousandYoung: If you go by the theory that the majority of the enemies are her former children.
* SayMyName: ISAAC!
* SkippableBoss: Provided you have the Bible on you by the time you reach her, and it's fully charged.
* TacticalSuicideBoss: It's not actually mandatory, but making her stomp herself is possible and deals lots of damage.
* VoiceOfTheLegion: Her dialogue consists of her screaming "Isaac" in a demonic voice.
* WombLevel[=/=]BiggerOnTheInside: After defeating her, you will unlock her womb as a playable level.
* YourSizeMayVary: Just how big is she? In the cutscenes, she's a normal-sized human being, but her underwear is the right size to be worn by a child visibly smaller than her, in the boss fight her leg is the length of the screen, and then her womb is big enough to have two entire levels in it, with her heart being larger than Isaac.

!!Mom's Heart/It Lives!
[[quoteright:147:https://static.tvtropes.org/pmwiki/pub/images/momsheart.png]]
[[quoteright:103:https://static.tvtropes.org/pmwiki/pub/images/itlives.png]]
->Debut: ''The Binding of Isaac''
Defeating Mom once unlocks the Womb in subsequent playthroughs. At the end of the Womb lies Mom's Heart, which, summons enemies like Mom does. Defeating Mom's Heart reveals a Chest with something special inside. But once it's beaten enough times, it will become "It Lives!", which is Isaac as a fetus for some odd reason.
----
* BattleThemeMusic:
** "''[[https://www.youtube.com/watch?v=Zj9Ck3mNP4o ...Be Done]]''" in the original, completing Mom's theme and serving as a fast-paced theme to match the intensity of the fight.
** "''[[https://www.youtube.com/watch?v=eCW3hHhN8V4 Ventricide]]''" in ''Rebirth'', echoing Mom's theme in leaning more towards darker guitar and pounding drums with a background choir, sounding far more sinister. The term "ventricide" in itself isn't real, but it would roughly signify "death of the womb", and could be seen as a {{Pun}} on "ventricle".
* BossBanter[=/=]SayMyName: Has the same voice lines as Mom.
* BossRush: It Lives has the ability to spawn {{Degraded Boss}}es such as Monstro, Larry Jr., and Chub to fight you alongside the enemies.
* BulletHell: ''Rebirth''[='=]s version shoots red tears nearly constantly throughout the whole fight, even when retreating to the back of the room.
* TheBusCameBack: The original Mom's Heart form, to an extent, in ''Afterbirth+''. While unlocking It Lives used to make it so that you can no longer fight Mom's Heart, ''Afterbirth+'' lets you fight Mom's Heart again in the Void, likely so that the Bestiary is completable for those who already unlocked It Lives. It also shows up as a possible boss encounter in the Womb stage of Greed mode.
* DamageSpongeBoss: Its lack of mobility is made up for by a big health bar. Its Eternal version in the ''Eternal Edition'' has ''even more''.
* EnemyWithout[=/=]FetusTerrible: It Lives is not just any embryo, it has been confirmed by WordOfGod to be Isaac's embryo.
* FlunkyBoss: Will summon enemies intermittently. It Lives ups the ante by spawning {{Degraded Boss}}es.
* GetBackHereBoss: Despite not moving, it accomplishes this by occasionally retreating above the screen and leaving you to deal with its flunkies for a while.
* MookMaker: Hides at the back of the room while it spawns normal enemies to fight you, then jumps back to the centre to spawn more.
* NotQuiteDead: It seems that Mom survived their fight, or at least her heart did.
* SkippableBoss: Using the Bible instantly kills it like it did with Mom.
* StationaryBoss:
** In the main game, all it can do movement-wise is pull itself upwards to hide from attacks, making bombs very useful against it.
** The Eternal form in the ''Eternal Edition'' averts this greatly; it will pursue you relentlessly around the room until it dies, still spawning enemies.
* TacticalSuicideBoss: In ''Rebirth'', it moves to the top of the screen instead of disappearing entirely. Anything that wanders up there, enemies included, takes damage.
* TrueFinalBoss: Was initially this to Mom's FinalBoss. However, this is subverted by the Halloween update, and further subverted by ''Wrath of the Lamb'' and ''Rebirth'', to the point that it's no longer anywhere ''near'' the real final boss.

!!Satan
[[quoteright:144:https://static.tvtropes.org/pmwiki/pub/images/satan.png]]
->Debut: ''The Binding of Isaac''
The original TrueFinalBoss (although this isn't true as of ''Wrath of the Lamb'' and ''Rebirth''), Satan himself is the boss of what was originally the game's secret floor. Despite offering [[DealWithTheDevil Deals with the Devil]] throughout the game, he turns on Isaac and tries to kill him. His boss fight is comprised of three phases, detailed below under SequentialBoss.
----
* AttackOfTheFiftyFootWhatever: His final form is him flying far above the screen and stomping on Isaac with giant feet a la the Mom boss fight.
* BattleThemeMusic:
** "''[[https://www.youtube.com/watch?v=PhMj9tMtRs8 Enmity of the Dark Lord]]''" in ''Wrath of the Lamb'', an epic-sounding theme with techno and bells, along with heavy emphasis on bass.
** "''[[https://www.youtube.com/watch?v=Yq01zDqEOec Hericide]]''" in ''Rebirth'', a theme with heavier guitar and OminousLatinChanting, along with a deep voice growling demonically. "Hericide" roughly means "death of the master/teacher/lord".
* BlackSpeech: During the fight with him, he sounds somewhat like this. They are actually Mom's quotes, played backwards and in a much lower tone.
* DealWithTheDevil: He offers them throughout the game before you reach Sheol. Possibly even as you reach Sheol or after, if you have a Joker card on hand.
* EvilLaugh: Since he uses Mom's voice clips, he can do this.
* FaustianRebellion: Even if you do a ton of deals with him, you can still kill him (and the power ups from said deals can make it all the easier).
* FlunkyBoss: His first form is spawning the Fallen to fight you instead. His third phase continuously spawns Kamikaze Leeches.
* FrickinLaserBeams: His second phase can fire dual Brimstone lasers from his hands (that can curve), or a single one from his mouth.
* GiantFootOfStomping: His third phase has him attempting to crush Isaac with his giant hooves. They work like Mom's, but he does it much faster.
* LivingStatue: His second form is a unique boss where the statue of Satan comes to life, grows much larger, and attacks Isaac with tears and lasers.
* TheManBehindTheMan: Implied; after all, he did at the very least string Isaac along through the [[DealWithTheDevil Deals]] he makes in the devil rooms earlier on, before turning on Isaac at the last minute.
* {{Nerf}}: Satan's legs in his third phase no longer deal contact damage in ''Rebirth''.
* NoSell[=/=]PressXToDie: Using the Bible on him, which killed Mom and Mom's Heart instantly, kills ''you'' instantly instead. The same applies to later bosses, too.
* OneWingedAngel[=/=]SequentialBoss: Has three forms (see FlunkyBoss, LivingStatue, and AttackOfTheFiftyFootWhatever respectively).
* {{Satan}}: It's in his name, and he looks the part as well.
* SayMyName: Satan's battle cry when you defeat his first phase is Mom's BossBanter, only lower pitched and in reverse.
* SequentialBoss: Three phases: first a fight with The Fallen, then a fight with Satan himself on the ground with you, and finally a fight against his giant stomping legs.
* TacticalSuicideBoss: Those leeches he spawns don't just hurt Isaac.
* ThemeMusicPowerUp: When you fight the Fallen, his first phase, the regular boss theme plays. When Satan actually starts fighting, however, Hericide kicks in.
* TrueFinalBoss: He was the final boss of the game in the Halloween update, but this has been since trumped by ''Wrath of the Lamb'' and ''Rebirth''.

!!Isaac
[[quoteright:100:https://static.tvtropes.org/pmwiki/pub/images/isaacboss.png]]
->Debut: ''Wrath of the Lamb''
After beating It Lives, the Cathedral is unlocked. At the end of the Cathedral resides Isaac himself.
----
* AscendToAHigherPlaneOfExistence: Appears to do this upon his defeat.
* BaldOfEvil: Justified, being a young child and all.
* BattleThemeMusic:
** The original game had "''[[https://www.youtube.com/watch?v=H4noeZx9W6s My Innermost Apocalypse]]''", a techno-rock theme that involves a [[BossRemix sad reprise of the title screen music]].
** ''Rebirth'' gave him "''[[https://www.youtube.com/watch?v=Fr2BzEgwBwM Infanticide]]''", which is entirely centered around an OminousLatinChanting and heavy guitar, with the version in-game adding a OneWomanWail.
* BeamSpam: One of his attacks in ''Rebirth'' has him covering most of the room with beams of light, except for a couple safe spots in the corners. His third phase in old versions of ''Wrath of the Lamb'' had no attacks other than rapidly dropping the beams on random spots in the room.
* BoltOfDivineRetribution: Like Conquest, he can summon several pillars of light. The safe spot is in either corner of the room perpendicular to the direction the pillars are spawning.
* BulletHell: Fires bullets in all directions, and fires at you if you hit him. Having a high-fire rate can backfire horribly.
* ChildrenForcedToKill: A subtle example. While it's easy to miss, Isaac doesn't attack at all until he takes damage.
* CounterAttack: In addition to the projectiles he fires periodically, he also fires at you whenever you damage him. In ''Rebirth'', he constantly fires in your general direction when not using another attack, instead of only doing so when hit.
* DamageSpongeBoss: Later updates in ''Wrath of the Lamb'' made him this. ''Rebirth'' instead adds more BulletHell, and makes him mobile in his third form.
* EnemyWithout: Maybe.
* [[EvilCounterpart Evil Counterpart/Good Counterpart]]:
** He seems to be the latter to Satan. He appears in a Cathedral instead of Sheol, summons angels instead of demons, and has an angelic appearance.
** He could qualify as either to the PlayerCharacter. The fight against him is most likely more symbolic than literal anyway.
* FlunkyBoss: Spawns Angelic Babies, which is fitting.
* GoOutWithASmile: Well, he is smiling in his third phase.
* HolyHandGrenade: He can cover the screen in rays of deadly light.
* MessianicArchetype: His OneWingedAngel.
* MirrorMatch: He ''is'' Isaac. Note that he's not a MirrorBoss, as he can do things you'll never be able to pull off.
* PowerGivesYouWings: In his final form. An item called Fate can be unlocked, allowing the player to have those same wings.
* PurposefullyOverpowered: You know how almost all the items added to ''Wrath of the Lamb'' are much more powerful than the ones in the base game? ''There's a reason for that.''
* SequentialBoss: Three phases: one lying in the fetal position, one standing up, and one with wings and teleportation.
* StationaryBoss: For the original game and the first two phases in ''Rebirth''.
* TroubledFetalPosition: The first part of the fight.

!!???
[[quoteright:100:https://static.tvtropes.org/pmwiki/pub/images/bluebabyboss.png]]
->Debut: ''Wrath of the Lamb''
Completing the Cathedral with the Polaroid item allows Isaac to enter The Chest. At the end of this super-secret stage lies...the Blue Baby?
----
* BackFromTheDead: Is a post-mortem version of Isaac, naturally.
* BattleThemeMusic: While the original version of the fight in ''Wrath of the Lamb'' shared "''My Innermost Apocalypse''" with Isaac, ''Rebirth'' gave him a proper, original theme called "''[[https://www.youtube.com/watch?v=FT3sXT9x9CU Ascension]]''", which has discernible Latin lyrics and an aggressive rock beat with odd, creepy noises in the background at certain points.
* TheCameo: From Creator/EdmundMcMillen's flash series ''Dead Babies''.
* DivergentCharacterEvolution: In ''Wrath of the Lamb'', ??? was mostly an Isaac clone right down to having the same boss theme, with the only real differences being his ability to spawn flies and periodically shoot homing tears. ''Rebirth'' reworked both bosses, and ??? was thus given a more distinctive pattern, most noticeably removing the beams of light in favor of increasing the rate at which he spawns flies, and a unique boss theme. The distinction is most obvious in their reworked final phases: Isaac prefers to [[GetBackHereBoss fly away from the player]] at high speed while periodically teleporting away to saturate the room with beams of light, while ??? slowly flies towards the player while spawning flies and Pooters and occasionally teleporting into the player's face.
* FlunkyBoss: One way he varies from the previous boss is that he summons flies in addition to his other attacks.
* InvincibleMinorMinion: In ''Rebirth'', he gets a halo of flies, which block your tears.
* OrbitingParticleShield: ''Rebirth'' gives him two Eternal Flies to block tears partway through the fight. He also gains the ability to summon Pooters, which orbit him at high speed and can thus serve as shields in addition to attacking the player.
* PaletteSwap: He is very similar to the previous boss, Isaac, so most of the tropes above apply to him too. This resemblance is downplayed in ''Rebirth'' by giving him different attack patterns from Isaac.
* TeleportSpam: Utilized in his third phase in ''Rebirth'', with a tendency to reappear [[TeleFrag right on top of the player]].
* TrueFinalBoss: Of ''Wrath of the Lamb'', being the boss of the only sixth chapter in the game, and since beating him unlocked the game's real ending. Subverted in ''Rebirth''.
* WeaponizedTeleportation: Tries to teleport into the player during his third phase in ''Rebirth''.

!!The Lamb
[[quoteright:169:https://static.tvtropes.org/pmwiki/pub/images/lamb.png]]
->Debut: ''Rebirth''
Defeating Satan and completing Sheol with the Negative item allows Isaac to enter The Dark Room, a dark reflection of The Chest. The skeletal demon known as the Lamb is the boss of this stage, and it fights with powerful attacks.
----
* AllYourPowersCombined / ConfusionFu: The Lamb's volleys of shots mirror those of previous bosses. This, combined with how it switches the type of bullet with each volley, and that all of its bullets are the same colour, make it a very difficult opponent to predict.
** ShadowArchetype: The Lamb's attacks also resemble combinations that can be used by Isaac -- for example, Monstro's Lung plus Homing Tears. Its DetachmentCombat is a lot like the Pinking Shears. It even begins the battle in Isaac's crying position!
* TheAntiChrist: In the Bible, the Lamb was a symbolic reference to Jesus. In this game, however, the Lamb is an undead demonic creature fought after Satan. The implication is that this Lamb is an alternate, [[SatanicArchetype demonic interpretation]] of Jesus.
* BattleThemeMusic: "''[[https://www.youtube.com/watch?v=DWo3PQjxogQ&t=107s The Fallen Angel]]''", a dark, creepy, fast-paced song with an ominous choir and wail.
* BlackoutBasement: When the body on his second phase is defeated, the room will darken for a brief time.
* CreepyCoolCrosses: Specifically, an upside-down one on his forehead.
* DemBones: The Lamb is essentially a demonic skeletal child with curved horns.
* DetachmentCombat: His second form involves his head floating around the room attacking you while his body lies limply on the ground spawning flies and sometimes tossing out Monstro-style shots.
* DualBoss: His second form, in which his head floats around the arena and his body stays on the ground to summon Flies and fire off a burst of tears.
* FlashStep: One of his attacks qualifies as this.
* FrickinLaserBeams: His second form gains the ability to shoot four-way Brimstone in the cardinal directions. He can also start rotating the beams like Mom's Heart/It Lives.
* HornedHumanoid SkullForAHead: He looks like an undead demon.
* LosingYourHead: During the second phase of the battle.
* MythologyGag: His name is a reference to the expansion for the original Isaac, named ''Wrath of the Lamb''. He is also visually similar to ''Wrath of the Lamb's'' horned skull logo. Given that Edmund had more planned for the original ''Isaac'', it's possible he was always intended to be the last boss of the expansion, but Flash's limitations meant he couldn't add him in.
* NightmareFace: Its skeletal face isn't pleasing to look at, especially in the vs. screen.
* OffModel: The Lamb's portrait in the versus screen is dark in colour, but in-game and in the ''Afterbirth+'' trailer, The Lamb is coloured white.
* SequentialBoss: Has two forms.

!!Mega Satan
[[quoteright:259:https://static.tvtropes.org/pmwiki/pub/images/megasatan.png]]
->Debut: ''Rebirth''
In ''Rebirth'', a giant golden door appears in the Chest and Dark Room stages. This door can be unlocked with a special item, which leads to ''Rebirth''[='=]s ultimate boss battle.
----
* AttackOfTheFiftyFootWhatever: Although the name probably gave it away.
* BattleThemeMusic: Shares "''Hericide''" with his own original form.
* BossRush: He summons bosses as he takes damage, and more if you don't do enough damage fast enough.
* BraggingRightsReward: Besides unlocking the final and definitive ending, there is no reason to fight him other than to boast you did it. The only thing you get out of winning is a new picture for your save file. There are no associated item or character unlocks, not even a mark on the character file to indicate that character beat him. [[AvertedTrope Averted]] in ''Afterbirth''. He gets both character unlocks and a mark on the sticky note upon beating him, and beating him on hard mode is required for getting the final item (or co-op baby, in the case for everyone except The Lost) for every character.
* BulletHell: What some of his attacks delve into.
* CognizantLimbs: His hands.
* DamageSpongeBoss: He's just shy of Hush in terms of overall health, and his individual forms have as much or more health than any other boss save Ultra Greed. He could actually be considered to have more health than any boss if you include the health of the mandatory boss fights. However, Mega Satan doesn't have the same damage-scaling property of those two, so he's functionally a whole lot weaker than they are.
* FinalBossPreview: Regular Satan's third phase can be considered this. In Sheol, you only fight his lower half. In the Chest/Dark Room's secret room, you face the much more difficult upper half.
* FlunkyBoss: Summons The Harbingers, the Super Sins, and fallen versions of the Angels. If you take too long on one of his phases, he starts summoning regular Sins and lesser bosses such as The Hollow and Fistula.
* GiantHandsOfDoom: Accompanied by a giant head. The hands serve mainly to [[ShieldedCoreBoss block shots aimed at the head]], which is treated as the main boss.
* GuideDangIt: The only in-game hint you have to his existence is "The Angels await!" You're supposed to bomb the Angel statues in the Angel Rooms, prompting them to engage you; both will drop a piece of a Golden Key on defeat, and getting both pieces opens a Golden Door in the Chest/Dark Room that leads to Mega Satan.[[note]]The Golden Door also only appears once you have completed the key for the first time, which is a GuideDangIt in and of itself.[[/note]] Fortunately, completing the key also unlocks "Dad's Key" as a regular item, which can also be used on the Golden Door for future playthroughs [[note]]The "Get Out of Jail Free" card also works[[/note]].
* InterfaceScrew: The only boss [[note]]Besides the Mask Of Infamy in the original[[/note]] who doesn't have a health bar, in either form. Averted if you have the Spider Mod item, which gives him a Spider Mod health bar.
* MarathonBoss: He has two forms, each of which has as much if not more health than every other boss excluding Hush and Ultra Greed. This is on top of all the other bosses he summons. Winning takes several minutes at least, and that's if you have a good enough run.
* RedEyesTakeWarning: Considering he was the TrueFinalBoss of the game before the title was being uplifted by Delirium, you ''will'' want to take warning.
* SealedEvilInACan: Heavily implied to be sealed by the beings in the Angel Rooms.
* SequentialBoss: Including his summons, he has ''twelve'' phases.
* SoundtrackDissonance: Due to a bug, doing too much damage to any form will cause the calm, somber "boss defeated" music to start playing. This was eventually patched.
* TrueFinalBoss: The second to last True Final Boss of the game (which is saying something, considering there have been ''seven other candidates'' before it), hidden at the final stage and having an extra unlock process required each run. Delirium took over the role in ''Afterbirth+'', but even then it is the final boss of an alternate route that also has a 50% chance of being available from Mega Satan.
* TurnsRed: Has two full health bars, and when you take down one of them, he really cranks up the BulletHell.
* WaveMotionGun: If you stand in front of him for too long, he'll charge up a gigantic blood laser for a long time, making his head nigh-impossible to shoot.

!!Hush
[[quoteright:185:https://static.tvtropes.org/pmwiki/pub/images/hush.png]]
->Debut: ''Afterbirth''
Defeating Mom's Heart or It Lives in under thirty minutes of total play time unlocks a short, hidden area[[note]]displayed as ??? in-game but generally called the Blue Womb or Dead Womb[[/note]]. This area only has one enemy: Hush, which appears to be another PaletteSwap of the Isaac and ??? bosses. Then he enters his ''second'' form, which is soundly described below.
----
* AttackOfTheFiftyFootWhatever: According to Edmund, it's a giant ??? pushing through the floor.
* BattleThemeMusic: Its first phase shares "''Ascension''" with ??? (because according to Edmund, it ''is'' ???), before it transitions to the heavier and oppressive "''[[https://www.youtube.com/watch?v=rbflsmpA69c Morituros]]''" when Hush's true form emerges.
* BodyHorror: Hush represents Isaac suffocating inside the chest; unsurprisingly, its "face" looks like it's being asphyxiated inside a bag.
* BonusBoss: Hush is sort of the "Isaac" counterpart to Mega Satan. While beating it does grant you a new ending, it doesn't require you to end the game. Instead, you can opt to go to Sheol/Cathedral once the fight is over. This was later patched out; defeating Hush now plays the ending and ends the run, but only the first time you beat it.
** Averted as of ''Afterbirth+''; beating Hush is the only guaranteed way to reach the Void and fight [[TrueFinalBoss Delirium]], and is required to actually unlock the Void.
* BulletHell: Its attack patterns during its second form. They even resemble the dense ring-patterns found in ''danmaku'' shooters like the ''{{Franchise/Touhou}}'' games; fortunately, the projectiles fired by these attacks are some of the slowest in the game.
* DamageSpongeBoss: Has the second highest health of all bosses in the game. Furthermore, its defenses scale with your damage output, so no matter what items you have, it'll take a long time to wear down. Combine this with its numerous BulletHell attacks and absurd enemy spawns, and you have a brutal boss fight.
* EldritchAbomination: As an embodiment of impending death by suffocation that looks like a giant face molded from blue flesh.
* FlunkyBoss: Begins spawning hordes and hordes of minions as the battle goes on.
* MarathonBoss: Hush has 6666 health and has a damage resistance mechanic which hardcaps how much damage you can do at once. Even an overpowered build will still take ten minutes to kill this thing.
* MeaningfulName: To hush is "to put at rest", and seeing as this boss represents Isaac slowly suffocating in the Chest, the name is ''quite'' appropriate.
* NumberOfTheBeast: Its base HP is 6666.
* OcularGushers: When low on health, Hush will fire out geyser-like streams of tears from its eyes that track you like a pair of KillSat [[FrickinLaserBeams lasers]].
* SequentialBoss: Fights like Isaac and ??? at first, but then it teleports away and its huge face comes out of the floor, firing loads of bullets.
* StationaryBoss: Mostly. It begins laying on the ground, as a variant of Isaac and ???, then turns into a large bullet-spewing head. The head can move around, but generally, it stays still when attacking.
* SuspiciousVideoGameGenerosity: Before the fight, the game gives you two item rooms, four golden chests, and a shop. Needless to say, ''you will need them''.
* ThemeMusicPowerUp: The first phase of the fight has ''Ascension'' playing in the background. Once the second phase begins, the music changes to Hush's own theme, ''Morituros''.
* TrickBoss: Shares a boss theme with ??? and fights like him, with a health bar that goes all the way down to zero, so you'd think that's all there is to him. Nope.
* WrapAround: It fires shots that go out of the room and then come back from the other side. Notably, these shots actually get ''faster'' after the wrap-around.
* ZergRush: Easily spawns more enemies than any other boss in the game, throwing entire floors' worth of flies, Gapers, and Boils at you throughout the fight.

!!Ultra Greed/Ultra Greedier
[[quoteright:161:https://static.tvtropes.org/pmwiki/pub/images/ultra_greed.png]]
->Debut: ''Afterbirth'' (Ultra Greed)\\
''Afterbirth†'' (Ultra Greedier)
The final boss of Greed Mode fought in a stage named after him. A giant version of Greed that uses coins to attack, summon minions or heal. ''And he still makes you drop money when hit''.
----
* AnimationBump: Ultra Greed moves around a ''lot'', and the animations are ''extremely'' smooth and detailed.
* AttackOfTheFiftyFootWhatever: A massive variant of Greed.
* BanditMook: Like his smaller versions, his attacks will cause you to drop money. Unlike the others, however, he will actively pick up the money you drop, which heals him slightly.
* BossRemix: "''[[https://www.youtube.com/watch?v=mhdlLlRMH_c Chorus Mortis]]''". It incorporates elements of the shop and arcade themes, the latter of which is, itself, a remix of the title screen.
* CripplingOverspecialization: Ultra Greedier uses almost nothing but explosive attacks. With Pyromaniac or the Host Hat, he is literally incapable of harming you outside of contact damage and highly telegraphed lasers.
* DamageSpongeBoss: His health is slightly higher than that of Mega Satan's first form, making him third overall, and the damage scaling means he'll last a whole lot longer.
* DefendCommand: One of his abilities is to shield himself with his arms, reducing all damage dealt to him, which he usually uses when he has flunkies or bomb coins active.
* FanDisservice: [[https://bindingofisaacrebirth.gamepedia.com/File:Boss_Ultra_Greed_back.png Has a large, visible, and well-detailed butt]]. He's also a massive corpse-like monster that ultimately has a little boy as the base of his design, and might even ''be'' an alternate version of a little boy.
* FinalBoss: Of Greed Mode.
* FlunkyBoss: Can spawn Keepers close to himself, call more minions from the arena's doors, and drop a bunch of large coins that will cast buffs on him if they're not destroyed.
* FrickinLaserBeams: In his second form, the doors shoot gold Brimstone beams whenever he pounds the ground.
* TheGambler: His primary attack depends on the outcome of a slot machine. Although it's not ''that'' much of a gamble since every outcome is pretty terrible for you. You're just hoping that he gets one of the ''less'' terrible ones.
* KingMook: To Greed and all of his mook counterparts.
* MadBomber: One of his slot machine attacks is to drop giant bomb coins all over the arena. Ultra Greedier gains an explosive effect on all of his attacks.
* MarathonBoss: His health is about half that of Hush, but he shares the same damage reduction mechanic to prevent you from winning too fast. Furthermore, he has the ability to heal during the fight, though not by much. Greedier Mode is even worse, as there's the second half to his fight.
* MoneyToThrowAway: Uses large coins as projectiles. At times, huge ones fall from above. They can explode, heal Ultra Greed, or allow him to summon minions if you don't get rid of them.
* NoCureForEvil: A notable aversion. He's unique in his ability to heal through heart coins, though it isn't very much. He'll also heal a little if he picks up the coins you drop.
* PaletteSwap: Ultra Greedier, Ultra Greed's gold-colored form.
* SequentialBoss: In ''Afterbirth+'', he becomes this in Greedier Mode. After beating his first form, his statue (now called Ultra Greedier) will start attacking.
* SpinAttack: Does spinning lariats when you're close.
* StoneWall: His attacks, unlike most other final bosses, don't employ BulletHell and are comparatively easy to avoid. He makes up for this by being able to tank attacks that only Hush could withstand, with his damage reduction ensuring that he will always last for a few minutes. The challenge comes not from dodging him, but from ''outlasting'' him.
* TacticalSuicideBoss: Downplayed compared to most examples, but his bomb coins can damage him as well. He uses his DefendCommand to block most of the damage. His second form is even worse in this regard since all of his attacks have explosive properties and he no longer defends. Half of the time you won't land the final hit that kills him.
* TakenForGranite: Ultra Greed turns into a solid gold statue when killed. Midas' Touch (touched enemies temporarily turn into gold) applies a penalty to his damage scaling property, letting you deal greatly increased damage. In Greedier Mode, he keeps attacking as a statue and explodes into a fine gold dust on death.
* TurnsRed: As he loses health, his attacks become faster and he spawns more giant coins, which also take effect more quickly. He also visually becomes redder as an indication of this. He also does this whenever heals via the Heart Coins from his slot machine or by picking up coins; the more he heals, the redder he gets. This is only temporary, however.
* YourPrincessIsInAnotherCastle: On your first run through Greedier Mode. So you've beaten Ultra Greed, he's turned to a statue, and you wait for the Greed Machine to spawn... but it doesn't, and after a long pause, Ultra Greed's statue starts attacking you. This new form is appropriately called Ultra Greedier. He doesn't bother with the pretense on subsequent runs and will begin attacking in his statue form almost immediately.

!!Delirium
[[quoteright:192:https://static.tvtropes.org/pmwiki/pub/images/portrait_delirium.png]]
->Debut: ''Afterbirth†''

The final boss of an area added in ''Afterbirth†'', the Void. Beating Hush will unlock a floor made up of various different environments from the game, with this as the boss of one of its several boss rooms. It first appears to be a giant, melting skull, but will shift forms to white variations of the previous bosses.
----
* AmbiguousGender: Being less of a "person" and more of a manifestation of a mental breakdown that can change into almost any other boss from the game that takes the form of a gigantic skull, it's difficult to tell if Delirium even has a gender in the first place. A Tweet from Edmund [=McMillen=] during the promotion of ''Four Souls'' refers to Delirium with "him", however.
* AllYourPowersCombined: This is the boss' primary attack method. It will randomly transform into almost any other boss found throughout the game (including some of the other final bosses!) and take on the transformed boss' attack patterns, all while still firing off its own bullet rings. Once it TurnsRed, it will shift through bosses much faster, and each form attacks far more quickly.
* BattleThemeMusic: The eponymous track, "''[[https://www.youtube.com/watch?v=8mp3gNFN61Y Delirium]]''", which perfectly matches the increasingly fast pace of the battle, at one point sounding like it's skipping like a scratched CD.
* BerserkButton: Attempting to use the Chaos Card on it will not only fail, but also make it temporarily turn red and attack much faster.
* BulletHell: Despite them being more simple, Delirium's bullet patterns manage to be worse than Hush's because it shifts into random bosses you've encountred in the run to change the pattern around, plus [[TeleportSpam it never sits still]]. This is on top of Delirium's own unique bullet patterns being fired from the bosses along with their modified patterns. By the time you've got it down to 1/4 health, it'll be firing off a new pattern before the last one even finishes.
* ContractualBossImmunity: The single enemy who isn't harmed at all by the [[OneHitKill Chaos Card]]. In fact, all it does is piss Delirium off. Plan C (kill everything then yourself three seconds later) ''does'' technically kill Delirium, but its death animation is so long that Isaac will die before Delirium does. Lazarus is the only one who can get around this thanks to his ability to resurrect in the current room (Lazarus' Rags on another character will work, but Lazarus still gets the credit).
* DamageSpongeBoss: Clocks in at a whopping '''10,000 HP''', though it mercifully doesn't have the same damage scaling that Hush and Ultra Greed do.[[note]]Well, technically, it ''does'', but the scaling resets every time it transforms, so its {{damage reduction}} is hardly even noticeable.[[/note]] Even so, it teleports all over the place, so expect to spend a ''long'' time trying to kill this thing.
* DefeatMeansFriendship: [[MindScrew It's not clear whether or not they're the same entity]], but upon defeating Delirium for the first time, the player unlocks Delirious (spawns friendly bosses on their Delirium form to fight for Isaac) and Lil' Delirium (shapeshifts into one of a handful of different familiars and wins its effects).
* DyingDream: This creature, its environment, and the ending you get for defeating it drive home the point that most of what is seen during the game was Isaac's dying hallucinations.
* EldritchAbomination: A physical manifestation of a complete mental breakdown? Yeah, it qualifies.
* EyesDoNotBelongThere: When transformed into The Husk or Conquest, Delirium will have a single eye or a pair of eyes respectively inside its mouth. Its Teratoma form also has an eye inside.
* FinalExamBoss: It's only able to transform into bosses you've previously encountered during your run; thus, learning how each boss attacks is vital for surviving the fight with Delirium.
* FlunkyBoss: Can spawn minions depending on what form it is in. Bizarrely, when it becomes the Haunt, it will often transform into a single Lil' Haunt instead, the only instance of Delirium assuming the form of a regular enemy rather than a boss. A bug also causes its health bar to disappear when this happens, but he can still be damaged in this form.
* GetBackHereBoss: With a 2x2 arena to fight in, you'll spend a fair portion of the fight trying to figure out where it teleported to. This isn't helped by it transforming into wall-hugging bosses like Mama Gurdy or extremely small ones like Isaac.
* GlowingEyelightsOfUndeath: Has yellow pinprick eyes.
* InterfaceScrew: Will occasionally cause the arena to glitch and shift from one tileset to another, causing static to briefly fill the screen in the transition. This can happen ''anywhere'' in the Void, but is far more likely to happen when fighting Delirium. It is a guarantee when Delirium is dying, but by that point, there is little in the room that can harm you.
* MarathonBoss: With its high health, constant teleporting, and shifting into whatever boss it feels like, you'll spend a large amount of time chipping this thing down to nothing.
* MeaningfulName: "Delirium" is a disturbed state of mind. The battle plays out in a deranged and bizarre way, almost like some sort of hallucination.
* MindScrew: It's a giant, melting skull that turns into the other bosses wildly and at random (many of which are considerably smaller than it), and it's encountered in an area made of all of the past floors and fails to keep a consistent theme. Considering the name, nature, and location of this boss, it's implied that the fight is Isaac's mind breaking down.
* MorphicResonance: Delirium retains its coloring and often its facial features regardless of what form it takes, allowing you to tell it apart if it happens to spawn another boss monster.
* MyLifeFlashedBeforeMyEyes: Delirium is a physical representation of the phenomenon, illustrated by its ability to shapeshift into bosses that you've encountered this run and its death animation, which plays back several moments from the current run.
* NightmareFace: A ''melting skull'' certainly isn't pleasant by any stretch of the imagination. And since its features are retained when it transforms, this can result in similar faces appearing on ''any boss in the game''.
* OminousVisualGlitch: Its level may cloak the screen with static, changing the setting of the room where that happened. After beating Delirium itself, the screen will flash with static and various images from earlier in the run for an extended period of time. In this case, the "ominous" is because it represents Isaac's mind breaking down.
* {{Shapeshifter}}: It can shapeshift into any other boss, taking on their attack patterns.
* ShapeShifterSwanSong:
** The less health it has, the more often it changes forms. At critical health, it can't stand still nor stay in a form for more than a few seconds!
** Interestingly, the ''arena'' suffers this too. During Delirium's death animation, the arena glitches and shifts between several different appearances, finally stopping as he dies. Just after beating Delirium[[note]]it changes if one leaves and re-enters the boss room[[/note]], the end result is always the Chest, as that is closest to the "reality" of where Isaac is at that moment.
* TeleportSpam: Can teleport around in any of its forms. As it loses health, this becomes more frequent, to the point that Delirium barely spends more than five seconds without doing it.
* TimedMission: Played with. If you want to guarantee access to the Void and thus to Delirium, you have to beat Hush, which means you need to beat It Lives before the 30 minute mark (or have Mama Mega! on that floor). That said, the portal to the Void has a chance to spawn after beating Mom or any subsequent boss, increasing as you go further. Mega Satan has a 50% chance at best. He's also the only boss for whom completion is tracked even on victory laps, however, so one valid strategy is to take your time gathering items on the first run, defeat The Lamb, and then [[CurbStompBattle speedrun through the victory lap with your items]] to reach Hush.
* TrueFinalBoss: Of ''Afterbirth+'', and as that is the last major update to the game ([[VideoGame/TheBindingOfIsaacAntibirth for]] [[AscendedFanfic now]]), the game itself. Defeating it earns you the final ending to the game. Oddly enough, however, you can encounter it way before Mega Satan thanks to how its requirements and the level progression are set up.
* TurnsRed: The lower its health, the faster it shifts between forms and teleports.
* WeaponizedTeleportation: Even more than the ??? boss; Delirium ''loves'' to teleport directly onto you.
[[/folder]]
!''The Legend of Bumbo''
[[folder: Bosses]]
!!Loaf
* BadBoss: He'll stomp across the battlefield, crushing and killing his own mooks without any regard.
* FlunkyBoss: Spawns Dips and Corn Dips.
* TalkingPoo: Well, he doesn't talk, but he's a giant monsterous humanoid poo.
* ToiletHumor: A poop-themed enemy named ''Loaf''. Definitely something to expect in a ''Binding of Isaac'' installment.
!!The Duke
* SuspiciouslySimilarSubstitute: He's this game's version of The Duke of Flies, even boiling down to having almost the same name. Although, unlike his predecessor, he shoots out bullets.
* FlunkyBoss: Just like The Duke of Flies, he'll spawn flies between attacks.
!!Peeper
* EyeScream: His eyes are detatched from his body and you can hit it to make it switch lanes.
* {{Expy}}: He's pretty much a skinny version of The Bloat, whilst also borrowing Peep's name. Although he lacks the brimstone lasers and jump attack, his eyes are always detatched and he shoots out bullets.
* RedEyesTakeWarning: If one of his eyes turn red, that means it's about to attack you.
!!Shy Gals
* TheDividual: There's three of them, though you only have to defeat one to defeat them all.
* CreepyTwins: Well, Creepy Triplets.
* {{Expy}}: Of [[Franchise/{{Mario}} Shy Guys]]. They also bear some similarities to Mask of Infamy.
* SameSexTriplets: They're all referred to as girls.
* WhiteMaskOfDoom: Which protects them, unless you manage to knock it off.
!!Dusk
* SpeedBlitz: He has quite a bit of movement points, starting at the end of the room and being able to move all the way up and attack you ''in one whole turn''. Be prepared to protect (or heal yourself) when fighting him.
!!Gibs
* BlobMonster: A giant cube of green slime containing organs.
* DemBones: Among the organs suspended in its body include some bones and a skull serving as its face.
* FlunkyBoss: Spawns small goo enemies.
* SicklyGreenGlow: It appears to be glowing, although it's most likely light reflecting through it.
!!Gizzarda
* DemBones: A skull and some bones inside some weird rotting purple goop...
* FlunkyBoss: Spawns flies.
* MightyGlacier: She only has one movement point, but has high health and can resist certain attacks each turn.
!!Sangre
* AttackItsWeakPoint: The red, glowing heart within its ribcage, which has to be exposed in order for you to hurt it.
* DemBones: It's a floating skeleton with a heart.
!!Pyre
* FlamingSkulls: It's one giant flaming skull that glows different colors.
* PuzzleBoss: You must match tiles based on the color of its fire.
!!Bygone
* FlunkyBoss: Spawns flies.
* OurGhostsAreDifferent: The ghost that spawns during its second phase, which bears a resemblance to The Lost and Delirium (albeit less "melty").
[[/folder]]
----

to:

History Characters / TheBindingOfIsaac