A list of characters who appear in The Binding of Isaac: Antibirth. Currently under construction, please contribute!
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.
- Break the Cutie: The entire premise of the game is one for him.
- Children Forced to Kill: Isaac has to fight and kill plenty of enemies just to survive, up to and including his own religiously psychotic mother. Or so it seems.
- Create Your Own Villain: 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. This gains some very interesting implications at the true ending of Rebirth, where it's revealed that Isaac becomes a demon or the Anti Christ inside the Chest. Did Isaac have darkness inside him all along, or did he decide to become evil after all the horror that he went through?
- 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.
- Dark and Troubled Past: 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).
- Dead All Along: 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 locking himself in the chest, then showing his self-loathing which led to this, and finally showing his tragic backstory through a heartbreaking Photo Montage. 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 he has long since been Driven to Suicide and that none of the game is even happening.
- Driven to Suicide: Isaac hangs himself upon finding Transcendence (a noose) in Ending 2. This is Played for Drama in the final few endings: After we see that Isaac has been Dead All Along 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.
- Dying Dream: Ending 20 reveals that the whole game is this, including the thought of his mother attempting to kill him.
- Enemy Without: 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.
- Full-Frontal Assault: Unless an item is picked up, Isaac is battling the monsters of the basement stark naked.
- Hilariously Abusive Childhood: Many of the level intermission vignettes have Isaac getting picked on by kids, being dressed in drag, getting shit as a birthday gift, 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 self-explanatory, and many of the food items aren't exactly fit for human consumption.
- It's All My Fault: The ending you get for beating the Chest seems to imply that 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 he does blame himself, and this is what ultimately causes him to be Driven to Suicide.
- Kindhearted Cat Lover: Whenever the player gets a Game Over, Isaac usually states in the diary that he will give what he collected to his pet cat, Guppy.
- Madness Mantra: BAD BAD BAD BAD I'M THE DEVIL...
- Sanity Slippage: 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.
- Then Let Me Be Evil: It is strongly implied that at the ending of Rebirth, Isaac becomes a demon or The Antichrist in order to deal with all the horror he went through, up to and including his mother.
- Troubled Fetal Position: Isaac's signature pose, which all but cements the kid as The Woobie.
- Walking Spoiler: Due to the endings revealing more and more of what is actually going on between him and his family, it's only a given.
For tropes relating to Mom as a boss enemy, scroll down to the section on major bosses.
- Abusive Parent: 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. Due to the true ending revealing that Turns out to be a possible subversion, depending on whether you see the between-level cutscenes are canon or not.
- The Bad Guy Wins: It's revealed that Isaac suffocated to death while inside the chest. She wanted Isaac to die because of an (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
- Big Bad: Ultimately subverted.
- The Extremist Was Right: She's a religious fanatic that appears to think that she's on a mission from God, which is clearly not the case. At least until the canonical end of Rebirth, strongly implying that Isaac either was or now is a demon. If you subscribe to the "just batshit insane" theory, then she's Right for the Wrong Reasons.
- The Fundamentalist: She's heavily Christian, and her hearing the voice of God is what kicks off the plot.
- Hidden Depths:
- Ending 13 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.
- Endings 15 and 17 suggest that in the end, she might be at least somewhat concerned about her son's well-being.
- Knife Nut: She's holding her knife in almost every cutscene she appears in, and you can unlock said knife as a usable weapon in-game.
- Maybe Magic, Maybe Mundane: Is she really hearing the voice of God, or is she just batshit crazy? The best we get from McMillen is him stating:It was never implied that [Mom's] insane. And if youre going by the Bible and you believe all the stories, then why wouldnt you think that its possible now for that stuff to happen?
- No Name Given: Unlike Isaac, even her first name is unknown.
- Offing the Offspring: Her ultimate goal.
- One Bad Mother: Bonus points for actually being the main character's mother.
New Playable Characters
- Always Identical Twins: Played with. Jacob looks like normal person while Esau has dark red skin but both have the same hair style.
- Anti-Frustration Features: Since they automatically use any cards and pills they pick up, picking up a red card would run the risk of that card being Suicide King. Thankfully, the developers realized this and made it so that Suicide King never spawns in a Jacob & Esau run.
- Amazing Technicolor Population: Esau is a dark red because the Biblical Esau was described as "red all over" when he was born.
- Can't Live Without You: If one of the brothers dies, both die, so neglecting one of them to make the other stronger is out of the question.
- Damn You, Muscle Memory!: The twins automatically use any pick-ups as Esau's "use item" button is "Q", the standard use pick-up item button.
- The Dividual: Both Jacob and Esau are controlled by the player and if one dies both die.
- Mechanically Unusual Fighter: The player now has to watch for two characters while making sure they both get stat boosts and learning how their item buttons work.
- Single-Minded Twins: Downplayed. Despite both brothers moving in unison both can/have to use separate items, and they can be controlled separately.
- Tears of Blood: Esau has these standard.
- Aerith and Bob: The only playable character with a name taken from a town instead of a character.
- Girlish Pigtails: She sports a pair tied up with blue ribbons.
- Magikarp Power: Bethany's inability to pick up soul hearts means that one would have less health over all, and needs to avoid taking damage period to have a good chance at getting an Angel/Devil room for the floor, to say nothing of the fancy dodging required to build up flames with Book of Virtues. However, the soul hearts function to get much more use out of her starting item, and with enough cleared rooms and/or soul hearts picked up, she could have a huge multi-layered tornado of flames that each fires a spectral shot on its own.
- Mechanically Unusual Fighter: As stated above, Bethany uses heart pick-ups to increase the counter to recharge space bar items. This lets her use space bar items more often at the cost of being more dependent on health increasing items and pick-ups. Any item that remove all of her hearts will kill her; for example Abaddon remove all of her red hearts and add the Black Hearts to the counter.
- Nonstandard Character Design: Bethany is the only playable character with a pair of eyelashes.
- Secret Art: Bethany is the only character capable of spawning white and black flames with Book of Virtues, by consuming Immortal and black hearts from her counter. Black flames can inflict fear with their shots, while white flames can regenerate themselves and other flames and their shots can block enemy tears.
- Action Bomb: Fly Bombs are literally just bombs with wings.
- Wreathed in Flames: Willos are flies on fire.
Dragonfly/Sick Boom Fly
- Action Bomb: Just like the other Boom Fly varieties.
- Deadly Gas: Sick Boom Flies release a cloud of poison gas on death.
- Playing with Fire: On death, Dragonflies will release waves of fire in 4 directions. The directions they hit depends on the Dragonfly's appearance: if their eyes are normal, the fire goes in the cardinal directions, and if they have "x" eyes, the fire will be launched diagonally.
- Invisible Monsters: Wraiths are permanently invisible, but (somehow) still leave reflections that can be used to track them. They're also revealed by the periodic flashes of lightning in the Downpour.
- Losing Your Head: They look like human enough, except they're missing the upper half of their head.
- Unique Enemy: Fanatics only appear in the Heretic's boss fight, and nowhere else.
- Counter Attack: They will spin and fire tears as they take damage.
- Gasshole: They attack by farting, although the Dumpling's farts only inflict knockback and don't damage you. Skinlings and Scabs upgrade to Fartillery due to their fart attacks actually being dangerous on their own.
- Shout-Out: Taken from Edmund McMillen's earlier games.
- Toilet Humor: They're basically floating butts that move around by farting.
- Breath Weapon: They attack by breathing a stream of purple fire toward Isaac.
- Action Bomb: Bubbles bursts into a fountain of tears on death, but it's easy enough to avoid as long as you don't run directly into it.
- Counter Attack: Bubbles spits tears on taking damage, while Vessel spawns Small Maggots.
- Dead Weight: Barfy and Vessel, being zombie Fatties.
- Dem Bones: Big Bony is a skeletal Fatty. Turns out they're big-boned after all.
- Underground Monkey: Several variants on the basic Fatty enemy.
- Action Bomb: Bouncers explode into multiple bullets on death. The salvo is a lot smaller if you manage to kill them before they inflate.
- Body Horror: As Mulligan varieties, this is a given for most of them. Of special note is the Bouncer, whose entire head is little more than a giant tumor that can inflate.
- Mook Maker: Prey spawns Small Leechers, Mullighouls summon Willos, and Blasters lob Fly Bombs.
- Asteroids Monster:
- Cursed Globins collapse into two piles of goo when killed, and each is capable of reforming into a new Cursed Globin. Thankfully, they can only duplicate a limited number of times.
- Cohorts split into several piles of Globin goo on death, which will naturally become Globins if not killed quickly enough.
- Enemy Summoner: One of the Cohort's attacks summons a goo-form Globin.
- Underground Monkey: Advanced varieties of Globins.
Black Knight/Loose Knight/Empty Knight/Pon
- Attack Its Weak Point: As with the other Knight variants, you damage these guys by attacking their exposed brains. The catch with the Empty Knight + Pon is that the brain is now hopping around outside the Knight.
- Attack Reflector: In addition to being immune to damage, the Black Knight's front end deflects tears.
- Detachment Combat: Killing a Loose Knight causes it to split into an Empty Knight and a Pon.
- Shoot the Medic First: Unless you focus down the Bishop first, you won't have much luck trying to damage enemies in the room.
- Support Party Member: They can only protect other enemies, and have no offensive abilities.
- Enemy Summoner: Both of them attack by summoning other enemies until killed.
Worms and Grubs
Small Leech/Small Maggot
- Aquatic Mook: Small Leeches only appear in the Downpour, and because the floor is covered in water, they can swim across gaps.
- The Goomba: Small Maggots crawl around very slowly and aimlessly, and pose very little threat. Unusually, these only start appearing in the Corpse, the final alternate floor.
Corpse Eater/Carrion Rider
- Cannibalism Superpower: Corpse Eaters can eat other enemies that cross their path, gaining a speed boost in the process.
Strider/Rock Spider/Tinted Rock Spider/Coal Spider
- Piñata Enemy: Like regular Tinted Rocks, Tinted Rock Spiders drop Soul Hearts on death. They tend to spawn when you bomb Tinted Rocks in the Mines.
- More Dakka: They fire a continuous stream of shots, similar to the effect of Soy Milk.
- Wall Crawl: As a Wall Creep variant.
- Rule of Three: Hardies can only use their charge attack three times; after the third time, they automatically crumble.
- Talking Poo: Well, it doesn't talk, but it's still a living coprolite.
- Balance Buff: They're one for the Clotty, giving them a powered-up fiery form and by extension making them immune to fire damage.
- Infernal Retaliation: They're formed when a Clotty catches fire, causing it to move and shoot much faster.
Floating Host/Hard Host
- Dishing Out Dirt: Hard Hosts attack by releasing rock waves.
- Invincible Minor Minion: They're more of an obstacle than an enemy, as they can't be killed and don't become inactive when the room is cleared.
Bomb Grimace/Quake Grimace
- Earthquake Machine: The Quake Grimace releases rock waves in front of it.
- Helpful Mook: Bomb Grimaces don't really count as enemies at all, as their only function is to give you bombs that can be picked up and thrown.
- Invincible Minor Minion: They can't be damaged, and don't deactivate under any conditions.
Blind Bat/Echo Bat
- Actually Four Mooks: Blind Bats are seen hanging from the roof by themselves, but once they're awakened, four of them drop down at once.
- Interface Screw: The Echo Bat can scramble your movement controls, which can be bad news when you're busy dodging three other enemies.
- Invincible Minor Minion: Can't be damaged, but will die if all other enemies are killed.
- Kaizo Trap: When they die after clearing the room, they also explode. Fortunately, there's a long enough delay before the explosion that you should be able to get away.
- Taken for Granite: Stillborns are composed largely of stone. They're inspired by the phenomenon lithopedion, which is where a fetus dies in the womb and becomes calcified.
- Enemy Summoner: Nightwatches appear in darkened rooms and hold lanterns; if they catch you in the lantern's beam, they'll lock the doors and disappear while leaving enemies in their place.
- Invincible Minor Minion: Nightwatch is invulnerable, but can be ignored as long as you stay out of their line of sight.
- Playing with Fire: Candlers periodically create damaging flames in their wake.
- Artificial Brilliance: Polties tend to make a beeline for any explosives in the room to try and get in as much damage on you as possible. And if you're expecting them to crack open a Tinted Rock for you, forget about it; the Polty will throw everything else in the room, then grab the Tinted Rock and run away with it.
- Improvised Weapon: Rocks, TNT, buckets, poop... if it's an obstacle that can be picked up, they'll use it as a weapon.
- Poltergeist: If the name didn't make it obvious, they're ghosts that pick things up and throw them at you.
- Invincible Minor Minion: Coils can't be killed normally, and will respawn if destroyed with a Chaos Card. Note that they will cause contact damage even if the room is cleared.
- Shock and Awe: They radiate electric beams that attach to enemies in the room. A number of rooms have these in combination with Wall Huggers and Sliders, leading to a lot of dodging with not much else you can do about it.
- Infernal Retaliation: Gyros will turn into Grilled Gyros on contact with fire, becoming faster and tougher.
- Our Monsters Are Weird: Even by the standards of this game, a wheel of meat that rolls around while attached to a bone is pretty out there.
- Deadly Gas: Release a cloud of poison gas around themselves that lingers for a few seconds after they're killed.
- Bullet Hell: Very mild compared to most examples in the game, but it shoots a lot of projectiles for a boss you can fight on the first floor.
- King Mook: Of various flies, most notably the bloat flies.
- Mascot Monster: Baby Plum is the mascot of the mod. Ironically, it is the only new boss that does not appear on any Antibirth floornote .
- Back from the Dead: It's an undead version of Polycephalus and The Stain.
- Ballistic Bone: It can launch sprays of bone projectiles.
- Dem Bones: A fully skeletal version of Polycephalus.
- "Get Back Here!" Boss: Like always, it pops up to attack and pulls away to hide.
- All Your Powers Combined: Reap Creep combines the abilities of all three varieties of Wall Creep in the vanilla game and turns them Up to Eleven.
- Beam Spam: Its third phase can fire a spray of four sweeping Brimstone beams.
- Giant Spider: It's a giant Wall Creep around the size of Widow.
- King Mook: Of the creeps.
- Mook Maker: Spawns a lot of creeps to harass the player. It can also shake spiders loose from the ceiling.
- Sequential Boss: Has three phases, each imitating a different Wall Creep, all with different attacks. Its first phase primarily fires long chains of bullets aimed at the player, its second phase shoots wide spreads, and its third phase attacks with Brimstone lasers.
- Boss Arena Urgency: It can punch holes in the floor with its tail. Given the way pits work in this game, this won't kill you, but it does make it more difficult to dodge Wormwood's attacks and gives it more places to ambush you from.
- Deadly Lunge: Gains a very fast one when it's at low health.
- Making a Splash: Its projectiles appear to be water, as opposed to the standard blood projectiles.
- Meaningful Name: Named after the biblical Wormwood, a star which will fall and turn a third of Earth's waters bitter and deadly.
- Turns Red: It becomes much more aggressive and will start making holes in the ground at low health.
- Underground Monkey: It's more or less an underwater Pin with five additional levels in badass.
- Flunky Boss: Just like the original Duke of Flies, but with small leeches instead of flies.
- Punny Name: "Beelzebub" + "blub", an onomatopoeia for bubbling water.
- Underground Monkey: A drowned, but still animate, version of the Duke of Flies.
- Battle in the Rain: The battle against him is accompanied by a constant downpour that stops when he's defeated.
- Dance Battler: His movements in battle borrow heavily from the flamenco.
- Making a Splash: Rainmaker's attacks all have him levitating balls of water to hurl at the player.
- Something About a Rose: He carries a rose in his mouth in the Versus Character Splash. In the fight itself, it's mostly absent except when he pulls it out after one of his attacks.
- Bedsheet Ghost: What's underneath its sheet is quite a bit scarier, however.
- Flying Face: That rips itself open to reveal a skull when its minions are dealt with.
- Flunky Boss: 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.
- Frickin' Laser Beams: In his second phase, he'll fire Brimstone downwards as he strafes along the top of the screen.
- HeelFace Turn: The Lil' Haunt item gives you a friendly Lil' Haunt who chases your enemies.
- Intangibility: Until his minions are dead.
- King Mook: To the Lil' Haunts.
- The Last of These Is Not Like the Others: All of the other bosses in the alternate route are either original to the mod or rehashed for it. The Haunt, on the other hand, is taken directly from the base game with no modifications. This is likely so that Downpour can have at least four bosses along with the other three new floors, as the new Basement/Cellar boss Baby Plum does not appear in the floor's alternate counterpart for whatever reason.
- No Fair Cheating: 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. Of course, if you're fast enough you can dodge it and still hurt the boss before it loops back.
- Our Ghosts Are Different: This one has a skeleton. Which he'll gladly show to you.
- The Pawns Go First: Sends his Lil' Haunt minions to attack you while he himself remains intangible. When they go down, then he fights you.
- Boss Arena Idiocy: The Tuff Twins start out covered in a rock shell that makes them impervious to attack and must be broken with explosions. Their boss room always happens to contain a number of Bomb Grimaces that provide free bombs to chuck at them, and occasionally a couple of TNT barrels as well.
- Flunky Boss: They spawn Inks (which release four bullets in the diagonal directions on death along with a puddle of slowing creep) to harass the player throughout the fight. If their head is exposed, they switch to Suckers instead.
- Shed Armor, Gain Speed: They become faster as you blow up their stone armor.
- Underground Monkey: Stone-encrusted versions of Larry Jr.
- All Your Powers Combined: Combines the abilities of all Grimace varieties in Rebirth and the new Quake Grimace in Antibirth.
- Easter Egg: Throwing a Chaos Card at him will instantly kill him,as well as open a hidden crawl space that holds several items and chests.
- Fire-Breathing Weapon: One of Gideon's attacks has it spewing fiery bullets down the middle of the room, which will leave lingering fires on the ground. It also exploits this by summoning a number of enemies that become more powerful when lit on fire.
- Flunky Boss: Summons six waves of enemies to attack you in addition to shooting at you himself. Defeating all of the minions ends the fight.
- King Mook: To the Grimaces.
- Nigh Invulnerable: Like the enemies he's based on, Great Gideon is immune to everything that's not a Chaos Card, and defeating the other enemies in the room causes him to shut down.
- Mad Bomber: His main modus operandi is to ride around on his minecart, chucking various bombs at you.
- Minecart Madness: Inverted. He's the one on the minecart, but you're still the one doing the dodging.
- Scooby-Dooby Doors: His boss room is lined with them, and Hornfel can emerge from any one at any time. Of course, the player can't use them.
- Screw This, I'm Outta Here!: Depleting Hornfel's health destroys his minecart, at which point Hornfel will run for the nearest door. This makes Hornfel the only boss that can be defeated non-lethally, but you do get a chance at a bomb-based item if you kill him before he escapes.
- Shout-Out: The Brimstone bombs he uses are visually based on the grenades launched by the Iron Bomber, an unlockable weapon in Team Fortress 2 which was originally designed and submitted to the Steam Workshop by Kilburn (one of the mod's creators).
- Super Spit: His main non-bomb attack has him continually speeding up on his minecart, only to end up going so fast that he gets sick and projectile vomits in your general direction. The puke, of course, explodes.
- Trick Bomb: Hornfel's bombs use several different modifiers: he can throw Hot Bombs which leave damaging fire behind, Rock Bombs which send rock waves in the cardinal directions, and a unique Brimstone bomb that explodes into a four-way Brimstone laser.
- Kaizo Trap: After it dies, the fire in its eye falls to the ground and erupts into a four-way burst, possibly damaging you if you're not paying attention.
- Non-Human Undead: It's an undead ghost. Try to wrap your head around that.
- Our Ghosts Are Different: And apparently more undead.
- The Pawns Go First: Just like the Haunt, the Heretic will send its minions after you first and only start fighting once they're all dead.
- Reflecting Laser: His boss room always comes with a number of extinguished fireplaces. One of his attacks lights them up, then fires a Brimstone beam that chains between them.
- Ungrateful Bastard: It gets revived by cultists, and it thanks them by turning them into Mooks to send after you.
- Attack Its Weak Point: Initially, it's the chain holding the two together; afterwards, the heart itself becomes the weak point, and the mask can be incapacitated by attacking it from behind.
- Cat-and-Mouse Boss: As with Mask of Infamy, the heart flees while the mask tries to run you down. The difference is that the heart is fully capable of fighting back, and the mask doesn't like to stay dead.
- Dual Boss: As opposed to the original Mask of Infamy which is taken down one part at a time, both parts of The Visage attack simultaneously, and even come with a number of Combination Attacks.
- Grappling-Hook Pistol: The Visage's heart can use chains to pull itself to nearby surfaces. Note that this includes the mask and Isaac.
- Turns Red: Twice. Once when the chain is destroyed and gives the two parts of the Visage free movement, and a second time when the heart's health drops low and it changes its attack patterns.
- Variable-Length Chain: The chain binding the heart and mask together in the initial phase, particularly noticeable when the mask charges and stretches the chain to around twice its usual length. During the second phase, the heart uses one in a number of its attacks.
- Bullet Hell: Like a number of other bosses, The Siren can unleash a dense array of bullets in all directions. Her shots actually curve in the air, making them harder to dodge.
- Charm Person: Can steal your familiars with her voice and turn them against you.
- Enthralling Siren: Her singing can lure your familiars over to her side.
- Expy: Of, oddly enough, the Gorgun from Enter the Gungeon, having several similar attacks and a similar appearance.
- Power Parasite: Effectively copies the abilities of your familiars by charming them. Things can get very messy if she steals something like Dry Baby or Dead Cat.
- Stripped to the Bone: The Siren is rapidly reduced to an inert skeleton upon death. Destroying her skull unlocks a trinket.
- Attack of the 50-Foot Whatever: Her boss fight.
- Ax-Crazy: 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.
- Body Horror: 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.
- Boss Banter: ISAAAAAC!
- Death by Irony: Crushed by her own bible!
- Disc-One Final Boss: Demoted to this on your second playthrough and beyond. She's still a Disc One boss in the alternate path, but in terms of floor number, she's faced much closer to the path's final boss than the main path's end.
- Evil Is Visceral: Likely the reason her body parts are detailed and somewhat deformed.
- Evil Laugh: She lets out one every time she successfully damages Isaac.
- Eye Beams: Mausoleum Mom gains the ability to fire Brimstone beams from her eye.
- The Faceless: 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 subverted after you beat the Chest in WOTL or Rebirth, but only briefly. In photographs, to be precise.
- Fan Disservice: 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.
- Fat Bastard: As shown by her giant leg and the picture that shows up when using Mom's Bra.
- Final Boss: In your first playthrough. She's nowhere near the True Final Boss, though.
- Flunky Boss: She'll summon groups of random enemies to battle Isaac.
- Gameplay and Story Integration: Using the Bible instantly defeats her in her boss fight.
- Giant Foot of Stomping: Her main method of direct attack.
- Gonk: Same deal as normal Mom.
- Gross-Up Close-Up: One of her leg in the boss portrait, and one of her body in the picture that appears when using Mom's Bra.
- Humanoid Abomination: 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 size, and her arm can fit in a chest inside her heart inside her womb.
- Leitmotif: Matricide, as with normal Mom. Mom's Heart, on the other hand, gets a new one in Gloria Filio.
- Mook Maker: And these mooks are a lot harder than last time!
- Mother of a Thousand Young: If you go by the theory that the majority of the enemies are her former children.
- Say My Name: ISAAC!
- Skippable Boss: Provided you have the Bible on you by the time you reach her, and it's fully charged.
- Tactical Suicide Boss: It's not actually mandatory, but making her stomp herself is possible, and deals lots of damage.
- Trick Boss: Defeating her while holding the Knife Pieces throws you into a fight against Mom's Heart immediately afterwards.
- Underground Monkey: The version of Mom you encounter in the Mausoleum.
- Your Size May Vary: 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.
- Bullet Hell: Particularly notable is that one of its attacks has it sucking in bullets from the walls of the room.
- Combat Tentacles: Has two of these tipped with sharp blades that it uses to lash out at you or confine you to a certain part of the room.
- Faceless Eye: Its "head" consists of a single eye and nothing else.
- King Mook: To the Whipper enemies encountered in Mausoleum.
- Back from the Dead: Its third phase is effectively a decaying Mom's Heart.
- Body Horror: It's some sort of gaping mouth with a giant maggot and rotten heart inside. Not something that should be inside anyone's body.
- Sequential Boss: Has three separate phases.
- Stationary Boss: In all three phases.
- Unexpected Gameplay Change: The second and third phases use Crawl Space physics and controls, turning the game into a 2-D platforming shooter.
- Confusion Fu: Chimera has perhaps the widest range of attacks of any non-final boss in the game, which changes up in its second phase; as such, it can be a very unpredictable opponent.
- Fastball Special: In its first phase, it can throw Sick Boom Flies at the player. In the second phase, it throws its own head.
- Losing Your Head: Chimera's head detaches when it takes enough damage, turning it into a Dual Boss.
- Mix-and-Match Critters: It's The Cage with Gurdy Jr. for a head.
- Attack of the 50-Foot Whatever: The biggest boss in the game (barring perhaps Mega Satan, or Mom counting the unseen rest of her body), taking up the entire top wall of a 2x2 room.
- Back from the Dead: It's the rotting corpse of Mama Gurdy, grey from time.
- Body Horror: Oh yes. Not only is it a decayed version of a boss that's already pretty far in Body Horror territory, but when its head detaches, it exposes two more skulls where its shoulders would be.
- Bullet Hell: As expected of a Binding of Isaac endboss, but The Witness takes this to a whole new level.
- Evil Overlooker: Its boss portrait has the Witness looming over Isaac in this fashion, instead of the "facing Isaac from the side" view of every single other boss.
- Final Boss: Of the Antibirth content.
- Interface Screw: A minor example. The Witness's fight takes place in a quadruple-size room that is zoomed out so that the entire room is visible.
- Knife Nut: One of its attacks has it pulling out and throwing a gigantic knife.
- Marathon Boss: Downplayed. While the fight against it is still longer than a normal fight, it lacks the scaling damage resistance that the canon final bosses have, meaning that it's a relative Glass Cannon.
- Taken for Granite: After you finally kill it, it hardens over into stone.
- Turns Red: After you deplete its health bar once, its arms explode, and its head bursts out out of its body to keep attacking.
- Two-Faced: Half of its face has rotted down to the skull.