Video Game / The Binding of Isaac

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"The Binding of Isaac is a sick, disturbing, dark, blasphemous, offensive game... And holy shit, do I LOVE it! (...) Its dark, twisted sense of humor and hardcore gameplay won't appeal to everyone, but it WILL appeal to people who are AWESOME!"

The Binding of Isaac is a hybrid Roguelike/Zelda-like Top-Down Shooter made by Edmund McMillen and Florian Himsl, released in September 2011.

The story follows Isaac, a young boy who finds himself in possibly the worst situation imaginable. After his fanatical Christian mother begins hearing the voice of God, she removes all of his worldly possessions and strips him naked, confines him to his bedroom, and unhesitatingly accepts a commission to kill him in sacrifice to prove her devotion. Isaac discovers her intentions and manages to escape into the basement, where, still naked, he goes on the run as he fights off nightmares both physical and mental (using his own tears, no less), discovers secrets about his mother's past, and ultimately confronts her in an effort to survive.

An Updated Re-release, The Binding of Isaac: Rebirth, which overhauls almost every aspect of game, has since been released on PC, Vita and PS4 on November 4, 2014. It has a rather creepy trailer (and an even creepier one here). Rebirth boasts a new engine, a larger development team, even more items, better synergies between said items, and more new content. Ports for the Wii U, New 3DS, and Xbox One consoles have since been released in 2015.

The game also has a Spin-Off currently in development, titled The Legend of Bum-bo. The basic premise of the game is said to be a randomly generated RPG-like with a focus on puzzles.

Due to the surprising popularity of the game and the already large amount of content, multiple expansions have been released for both the original game and the remake:

  • Wrath of the Lamb is the very first expansion, released on May 28th of 2012. It adds a new category of collectibles called "trinkets," plus new and upgraded items, enemies, bosses, alternate areas, room types, a new character, a new ending and more. It has a trailer. Be afraid.
  • "The Binding of Isaac: Community Remix" is a fanmade overhaul Game Mod that adds multiple new items to the game (some from Rebirth leaks) as well as fixing descriptions, adding new music, and other such things.
  • Eternal Edition is another expansion to the original game, released by Florian Himsl on May 2015. The expansion features its own hard mode where almost every enemy and boss received an Elite Mook variant known as an "Eternal Champion". It's definitely as tough as it sounds.
  • Afterbirth, the remake's first expansion, released on October 30th of 2015. Not only does it come with the usual stuff (such as new items, bosses, and a new character), but it also features Greed Mode and even more alternative areas. Some of this new content are ideas suggested by the community; this includes items, challenges, and other features.
  • Afterbirth+, a smaller expansion for the remake, is currently due for a 2016 release. The expansion plans not only to include even more items and bosses, as well as another new character, but also features a detailed Monster Compendium, official developer tools and a Lua API specifically intended for modding the game.


Tropes found throughout the series include:

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  • 1-Up:
    • The 1-Up gives an extra life without drawbacks.
    • The Ankh gives you one extra life, but revives you as the Lethal Joke Character.
    • The Dead Cat gives you nine extra lives, but your health is set to one heart on pickup, retaining any soul/black hearts you may have. There's nothing stopping you from earning more, of course, but you also revive with only one heart.
    • Rebirth adds several more:
      • Guppy's Collar is similar to the Dead Cat, but with a catch. It has a 50% chance of giving you an extra life when you die, and has no limit to potential revivals, but can just as easily do nothing. In addition, you come back with only half a heart.
      • The Broken Ankh trinket behaves like the regular Ankh, but activates only about 20% of the time.
      • Judas' Shadow brings you back as a shadowy version of Judas who has a higher damage multiplier than his flesh counterpart, and counts as Judas for completion and achievements. Black Judas also starts with two black hearts, but can gain red heart containers normally.
      • Lazarus starts with the ability to revive. Regular Lazarus is fairly underpowered, with average stats and negative Luck, but once he dies, he revives into a better version of himself with a nice stat boost plus the Anemic item for the rest of the game, albeit at the cost of setting his Heart Containers to 1. Unlike other extra life sources, he will revive on the spot, allowing you to potentially finish off whatever killed you instead of having to start the room over again. Any other character with Lazarus' Rags lets them revive as Lazarus as well.
    • And in Afterbirth, dying while holding the Missing Poster revives you as the Lost.
  • 100% Completion: The "Golden God" achievement is obtained for getting all the items in the game. The "Platinum God" achievement is a step further: you need to collect all items from the vanilla game and Wrath of the Lamb. If you started off with the DLC, though, you're likely to end up getting both at the same time. Rebirth adds the "Real Platinum God". This requires beating both paths of the game with The Lost, who cannot gain HP in any way
  • 20% More Awesome: The video announcement for the Halloween update states that the game is now '20% more evil'.
  • Abnormal Ammo: Not just his tears, through upgrades Isaac can shoot: flies, blood, teeth, urine, chocolate milk, ghost tears, explosive vomit and more.
  • All Just a Dream: The first time you defeat Mom, the victory narration is revealed to be just a story Isaac is drawing. She's still coming.
  • An Adventurer Is You: Each of the characters is based on a stock character class.
  • And Your Reward Is Clothes: Did you beat Mom's heart? Congratulations, have a fez! ...What, you were expecting an ending?
  • Anti-Frustration Features:
    • Normally, treasure rooms are locked and require a key for entry. The exception is the treasure room on the very first floor, as there are few rooms on that floor, making the event of finding a key rather uncertain. Unfortunately, this is not the case if the player gets Curse of the Labyrinth, which combines the first and second floors into one. Here, both treasure rooms will be locked. Rebirth fixes this by unlocking both, which makes that curse a benefit on the first floor.
    • The No Damage Run achievements only require you to beat the bosses. This means you can take the shortest path to the boss rooms to avoid damage. It also takes effect when you beat the second boss, so you can go back after getting the achievement without having to worry about taking damage.
    • Pills can have negative effects, but not lethal negative effects. Health Down pills become Health Up if you are at one heart container or less and are not Blue Baby. Bad Trip becomes Full Health at one remaining heart total, unless you're Blue Baby, in which case it's at half of a soul heart. Number One causes any Range Down to become Range Up until the Womb.
    • Later levels can feature special rocks called keystones which cannot be bombed and instead can be "unlocked" with a key to get past them. If you are able to fly, keystones will be stuck in place no matter what, preventing you from accidentally wasting keys on them (although curiously they cannot be flown over).
    • Rebirth is all about making things more clear/less annoying, particularly for items which were previously poorly explained (most of the time) and just telling you how to unlock the majority of the characters, etc. This even extends to the game interface itself — each run lets you record seeds and play other seeds, the game keeps track of how far you've gotten with which characters (i.e. which major bosses beaten), and most significantly, autosave lets you resume where you left off if you close the game.
    • In Rebirth, if a room is literally impossible to clear (such as a single enemy being placed across a gap, but your range isn't high enough to hit it) and you don't have any explosive items to bomb open one of the doors, the doors in the room will open automatically after a while to make sure your run doesn't end prematurely.
    • Eternal Hearts are sandwiched between your red hearts and soul/black hearts on the health meter, giving the player a chance to build up a buffer to keep it safe until it can turn into a Heart Container.
    • Completing the extremely difficult Family Man challenge unlocks the extremely powerful Epic Fetus... and also unlocks the Glass Cannon challenge which starts you off with Epic Fetus, allowing you to immediately play around with the hard-earned weapon instead of waiting for it to come up in the game.
  • Artificial Stupidity: The Meat Boy familiar will eat your enemies for breakfast... if only it didn't occasionally kick bombs in your direction or get stuck chasing after and ineffectually biting enemies that are invincible (for example, the Mask part of the Mask-Heart monster). The Dead Bird has similar issues.
  • Ascended Extra: Isaac's pet Guppy is only seen in Isaac's will and some items. If you get three of said items, you turn into Guppy (giving you flight and the same fly-spawning ability as The Mulligan, if said ability was on steroids).
  • Asteroids Monster: Envy, Blastocyst, Fistula, and Teratoma, and to a lesser extent the double flies.
  • Attack Drone: Some of the of the powerups.
  • Awesome, but Impractical:
    • The Dr. Fetus powerup. Good luck trying to kill hosts with it. The Ipecac Syrup, added in the expansion, is even more Awesome But Impractical — it launches the same green spit bombs as the green enemies do. It can blow open doors and poisons enemies, but on the other hand, it travels in an arc that can make it very difficult to work with, especially on faster enemies. It also explodes when traveling over a rock, even when it's visibly meters above it, so it will blow up in your face. Of course, just like Brimstone, mastery of such items can make them Difficult but Awesome.
    • Several rare items, particularly in combination with each other, would be awesome... except finding them all in the same playthrough is unlikely due to the randomized nature of the game.
    • When Isaac is down to his last half-heart, The Scapular item grants a last-gasp reprieve of one soul heart. When combined with the Cursed Skull trinket (which teleports the player to a safe room when he has half a heart left), the player is functionally invincible at the cost of having to re-attempt the room he died in from the start. Good luck fighting bosses under no-hit conditions.
    • Technology 2 fires a constant laser that deals low damage, at the cost of a halved fire rate of normal tears. Normally, this wouldn't be a problem, but since Issac fires a shot every time you hit him, you'll face Bullet Hell and won't be doing nearly enough to compensate.
    • Crack the Sky causes several beams of light to strike the room, causing massive damage to anything they hit. The problem is IF: The beams are only one tile wide and strike randomly, making the instances where you use it and instantly flatten a boss the exception rather than the usual. It also does no damage against Isaac and Blue Baby.
    • The Crying Detonator combo. Using Sad Bombs, Bob's Brain, Anarchist's Cookbook (or Tammy's Head), Rubber Cement, and Ipecac leads to utter destruction. While it is far more powerful with the Anarchist's Cookbook, with the mere fact that there are exploding bouncing tears everywhere, even you can get killed very easily. Master this, however, and not even Mega Satan can stop you.
    • The MissingNo Item. Have fun getting your items and stats completely randomized at the start of every floor.
    • The Mega Blast. When you use it, you release a massive beam for 15 seconds, letting you utterly decimate everything for that period of time, and it even persists between rooms. The catch? It takes 12 charges to use (every other item requires 6 at most) and it's very difficult to unlock (Beat Mega Satan with every character, including the hidden ones!).
    • Ludovico Technique and Ipecac. While the poison and explosion damage can be very helpful as you can specifically direct it towards your target, it always comes back to you when it does explode, leaving you unable to deal the continuous damage that Ludovico Technique is known for.
  • Author Avatar: In an odd sort of way, Ultra Pride can be for both Edmund and Florian.
  • The Bad Guy Wins: In the epilogue, Isaac didn't kill Mom. She's still coming.
    • In Rebirth, one interpretation of the secret 16th ending is that Isaac was the Antichrist all along, Mega-Satan successfully corrupted him, and Mom really was hearing the voice of God.
  • Battle in the Center of the Mind: Every character in the game (except for Mom) is Isaac. Try and work that one out.
    • And now in Afterbirth, you can transform into Mom. Yeah...
  • Belief Makes You Stupid: Isaac's Mom emotionally abuses Isaac, and then tries to make him into a Human Sacrifice, because of her religious faith and belief God is telling her to do so. It's hard to put a positive reading on that display of "faith".
  • Biblical Motifs: And a storyline, and a ton of references. Plus, The Bible itself appears as a collectible item, with the Book of Revelations as a separate item.
  • Big Bad: Who it is is really, really, really convoluted. Is it God, ordering Mom to kill Isaac? Is it Mom, who's just imagining things? Is it Satan/Mega Satan, who's trying to awaken Isaac as the Anti-Christ and using Mom as his pawn? Is it some combination of the three?
  • Black Comedy: The entire game is front-to-back, blacker-than-black Dead Baby Comedy. Power-ups include the severed body parts of beloved pets (which act as damage-ups, given that the game weaponises tears), a wire coat hangar (a home-made abortion tool which amps up Isaac's tears), and various (possibly) aborted or otherwise dead siblings of Isaac's including Brother Bobby, Sister Maggy, and Harlequin Baby (who act as combat pets). Hell, there's even a Secret Character in the form of a cyanotic baby corpse.
  • The Blank: The angel statue that appears in Angel Rooms as an alternative to deals with the Devil. And the real Angels contained within.
  • Bloodstained Glass Windows: The alternative final (actually second-to-last) floor is a cathedral; be prepared for some intense fights in it.
  • Bloody Bowels of Hell: The game leans heavily towards this over Fire and Brimstone Hell.
  • Bloody Murder: Almost all enemies use weaponized blood to attack. With the correct upgrades, Isaac can too.
  • Bonus Level of Heaven: The Cathedral.
  • Body Horror: Most powerups do horrible things to you in exchange for their effects. In no particular order, you may grow tumors, become a living insect hive, a walking CDC nightmare, cry blood, prop your eyes open with toothpicks, jam implants into your eyes, and so many more.
  • Boring but Practical:
    • Flight. It doesn't directly help you kill your enemies, but being airborne suddenly means that many dangers are a thing of the past, like chasms, spikes, creep, etc. It even has a combat benefit in many rooms: being able to fly above a rock or a hole that enemies can't reach means that you're effectively untouchable by melee-only enemies, letting you pick them off safely. Even against ranged enemies your movement is unhindered by terrain, so you have significantly more room to maneuver with.
    • The battery allows you to charge up your item much faster than usual, if you stick around in combat for a while. Simply kill all but a single enemy, and dodge until you get all you can out of it. note 
    • The Charm of the Vampire item allows you to restore half a heart for every 13 enemies you kill. One type of enemy in particular, the Hemogoblins, can regenerate back from the point after they count as a kill for the purpose of this item. Like the above, it's a slow slog to max health, but there's a good chance it's worth the trouble. The same can be true when you're in the later levels and find an arcade. In fact, the more useful it is, the more boring it becomes.
    • The Book of Revelations is more or less this. On one hand, its only effect is to give you soul hearts (and make the Harbingers appear). On the other hand, its effect gives you soul hearts and it gives you more chances of getting Meat Boy. Depending on how many levels you play through, you can easily get more soul hearts than you have room to display, provided you don't take too much damage.
    • The Candle from Wrath of the Lamb is also more or less this. It shoots a small flame forward a relatively short distance, doing very decent damage to anything it passes through, enough to One-Hit Kill most normal enemies. It also has the shortest non-zero recharge rate of any activateable item in the game, i.e. a few seconds. You don't even have to clear the room first. This makes it EXTREMELY useful against anything large, armored, or slow/immobile. Oh, and it can damage Satan's second form while it's still in statue mode while you're fighting his first form. Not as impressive as the Doctor's Remote or the Necronomicon, but still extremely useful.
    • The Bloody Penny trinket. It sometimes gives you a half-heart whenever you pick up a penny or other coin. While not as useful/awesome as Maggy's Faith (free eternal heart at the start of each floor) or The Polaroid (gives you an emergency protective forcefield as well as letting you into the Very Definitely Final Dungeon), those dropped hearts add up, allowing you partially farm for keys, bombs, and money in the Arcade (Blood Bank trades hearts for money; Bloody Penny gives you hearts when you get money; Slot Machines sometimes give out bombs, keys, money, and hearts in exchange for money)
    • Things don't get more Boring but Practical than the Yum Heart. No damage, no room-wide effect, no awesome buffs, just a free red heart every few rooms or so, which can mean the difference between staying healthy in the last areas or limping around as a One-Hit-Point Wonder desperate to find more hearts somewhere.
    • Depending on your situation, the Box can be an absolute godsend. All it does is give you one of each consumable, a pill, a trinket, and a tarot card. No big damage ups or Hp increases (unless it spawns a soul heart, or gives you a positive pill). While it can seem like (and can very well be, depending on your drops) a Power-Up Letdown, in certain runs where the Random Number God doesn't feel like giving you much of anything, just having something like an extra key or bomb on hand can end up getting you access to the items you need to win. If you were fine on consumables and/or needed that damage/hp upgrade because you're starting to fall behind, however... Hope you brought your D6.
    • The Smart Fly/Revenge Fly. Certainly not the most glamorous familiar you can have, a tiny glowing yellow fly that doesn't block any shots. However, if an enemy so much as sneezes on you, it will start ripping apart every enemy in the room as fast as it can. It can even deal a steady stream of damage to most bosses and can save you from the brink.
    • There are a few power-ups in Rebirth that allow you to break rocks or other obstacles by walking into them. It doesn't sound all that useful at first, but then you factor in all the rooms where rocks serve as cover for enemies or can hem you in, ones with pick-ups on the other side of them, the blue rocks that can produce Soul Hearts or other items...you get the picture. This also saves you bombs for damage or finding secret rooms, and one trinket guarantees you a coin drop whenever a rock is destroyed (which works very well with certain Cast from Money type objects, such as Magic Fingers and Money = Power). Destroying certain rocks can have negative effects, but they're outpaced by the potential gains.
    • The Arcade almost always includes a Blood Bank (which allows you to exchange life for money, with a small chance at other prizes) and a Slot Machine (which allows you to exchange money for a random chance at getting pickups, including life). If there are a lot of hearts lying around a floor after you clear it, you can use the Blood Bank to turn the hearts into coins, which can be fed into the Slot Machine, which will usually give you some hearts, which can be fed into the Blood Bank for coins, and so on. With enough hearts or coins (or the Yum Heart + Nun's Habit, which charges the ability to refill your hearts every time you take damage from the Blood Bank), you can continue this process until one machine or the other blows up, usually yielding a useful item. You're also likely to collect a bunch of Bombs and Keys and probably some Pills and Tarot Cards, and there's no real downside to doing this every chance you get... except that the process is very, very tedious. (Which means you can forget about the Boss Rush in Rebirth.)
    • Several effects, like Piercing shots from the Cupid's Arrow and Triple shots from using Inner Eye are boring, but useful in most situations, with the boring part leaving when you get both.
    • How to Jump in Rebirth. It's an unlimited use spacebar item which allows Isaac to jump over any obstacles for a short distance, essentially granting poor man's flight. It's also surprisingly good for dodging enemy attacks (especially the bosses who employ Bullet Hell). And since it has no recharge whatsoever, you can spam it with the Broken Remote (a trinket that teleports you every time you use a spacebar item) to freely access almost every room in the game, including the I AM ERROR room.
    • Shooting the poop and fires in every room. Most of the time, you get nothing. But sometimes, you get hearts, money, sometimes even the Petrified Poop trinket (which increases the chance you'll find something in the poop, even super-rare pickups like eternal hearts). When you're low on health, but have plenty of time, shooting the poop can be a life-saver.
    • The Placenta item from Rebirth. It immediately gives an extra heart container on pick-up, and will slowly restore your health... at a rate of half a heart every few minutes. If you're low on health and have exhausted every other option, this item lets you gradually regenerate to full health just by leaving the game on for half an hour or so while you physically get up and do something else to pass the time. (No, TV Tropes is not an option unless you have another device; clicking out of the game pauses it.)
    • Orbital familiars in general, including the lowly Pretty Fly. They rarely deal much damage and don't give you health, but they do block projectiles from hitting you — quite often if you obtain three of them. And if you do have the ability to turn invincible, most oribtals can be used as melee weapons.
    • Monstro's Lung. While it's a Spread Shot like its other items (20/20, Dunce Cap, Inner Eye, and Spider Shot), it's also an charge weapon that doesn't fare too well. Unless you add Tech-X, that is.
    • The Tech Items as a whole. While in some degree powerful, they (with the exception of X) all go in a straight line...unless you add the Ludovico Technique to either Tech or Tech 2.
  • Boss Bonanza: The Womb randomly has previous end-of-level bosses spawn in normal rooms. Sheol and the Cathedral have a much higher chance of these encounters. The Chest has a boss in every single room. And the same is true of its Rebirth-exclusive counterpart, the Dark Room.
  • Boss Rush:
    • Many of the bosses will also make encore appearances as Degraded Bosses; sometimes two at once. The challenge rooms become this in later levels.
    • Taken up a notch with Wrath of the Lamb's "Curse of the Labyrinth." This Random Event basically combines two floors, meaning you'll have to fight two bosses one after the other. There's also special challenge rooms that only spawn bosses, even at earlier levels (and they spawn harder bosses in later levels); these rooms are normally accessible only if the player has one or half a heart left.
    • Pushed even further with The Chest, The Very Definitely Final Dungeon. To elaborate, this floor is made up entirely of rooms containing two bosses that must be fought at the same time, which definitely helps to solidify this game's Nintendo Hard status.
    • And up a notch further in Rebirth: If you beat Mom inside of 20 minutes a secret room will open up in the wall leading to a giant room with four item pickups. Take heed though, pick up one and you have to fight almost every boss in the game coming in pairs with no escape but victory, death, or teleporting out. Succeed and you get another item. There's also the Dark Room, which is just like the Chest.
    • Finally, if you fight Mega Satan, you get to fight all of the Sins and the Four Horsemen, plus fallen versions of the two angels you bombed for the pieces of the key to get into the fight, all during the course of fighting the big boss himself.
  • Brain Monster: The game has enemies that are large brains that crawl around the floor, leaving a trail of blood that damages you if you step on it. There's also an even larger variant that splits into two smaller ones when it dies.
  • Breakable Power Up: The Wrath of the Lamb DLC introduces Eternal Hearts, which give Isaac half a heart's worth of health above his normal maximum. If he loses it, it goes away for good, but if he finds a second Eternal Heart or makes it to the end of the floor without losing it, it turns into a Heart Container and permanently increases his maximum life.
  • Breath Weapon: If enemies literally spitting flies at you doesn't count, then the SHOOP DA WHOOP item does. True to the meme it's named after, it allows Isaac to fire a single giant laser every two rooms.
    • There's also Brimstone, which is essentially a giant bloody laser of doom, and which Azazel gets a short-range version of as his default weapon.
  • Brutal Bonus Level: Sheol. Wrath of the Lamb also adds The Cathedral, and, if you beat The Cathedral while carrying The Polaroid, then The Chest as well. Rebirth adds the Dark Room, accessed by beating Sheol while carrying the Negative.
  • Bullet Hell: Things can get quite ugly with several shooting enemies on the screen.
    • In Rebirth, Mom's Heart has a firing pattern very reminiscent of traditional danmaku bosses, with slow projectiles that have wildly confusing trajectories. Then there's Mega Satan, especially in his second form, and Hush is practically an Extra Stage boss.
  • The Cameo:
    • One of the available powerups is a chunk of meat which, after collecting several, can be used to create a Meat Boy who will follow you and help fight enemies. There's an achievement for finishing him. Rebirth adds balls of bandages which become Meat Boy's girlfriend, Bandage Girl.
    • The walls of the Arcade are lined with posters of other McMillen games (like Time Fcuk).
    • Certain characters from other games make cameo appearances as alternate versions of boss fights, like Steven for Gemini, C.H.A.D. for Chub, Gish for Monstro 2, and Triachnid for Daddy Long Legs. The only alternates that aren't cameos are the plot important ones, It Lives and ???.
  • Cast from Hit Points:
    • The Devil Rooms, which exchange Max HP (or Soul Hearts) for items. There are also several items (such as Blood Rights and The Razor) that damage the player when used.
    • Eve, who runs on this and Critical Status Buff.
    • Wrath of the Lamb further builds upon this trope with spiked doors that lead to special red treasure chests, as well as sacrifice rooms and demonic beggars that reward the player for damaging himself.
    • Several items, like the Dead Bird and Red Patch, will only activate if Isaac takes damage.
    • And of course, the Kamikaze item. You can blow anything up, at any time...however, the bomb you use is stuck to you, forcing you to take damage in the explosion.
  • Cartoon Bomb: With a skull (or a trollface) on it.
  • Charged Attack: The chocolate milk enables a Hold-type attack. Brimstone is also hold-type. If you have both at the same time, they interact... oddly.
  • Checkpoint Starvation: Played straight in Vanilla, averted in Rebirth. In vanilla, a run needs to be completed in one sitting — you cannot save your run and leave the game, due to the limitations of flash. In Rebirth, due to being built entirely on a new engine, you can save your current run and come back to it at a later date.
  • The Computer Is A Lying Bastard: The item description for the item SMB Superfan reads "All stats up!". While the item does increase all of your other stats, it decreases speed.
    • That is actually a bug; SMB Superfan was intended to bring all stats up. There are other items that do lie about what they do, though. For example, the toothpicks item says "tears up" when it's actually a "shot speed up" item. Rebirth fixes all of these items, or changes the description to fit the effect.
  • Color-Coded for Your Convenience: Savvy players know to avoid anything that is green. Not keeping your distance will result in taking an explosive projectile to the face.
  • Competitive Balance: Each character is designed with this is mind.
    • Isaac/The Warrior aka, Jack-of-All-Stats: Isaac is not really effective at anything, yet has no real downsides. Any item can be possibly played in his advantage, and a good Isaac player will take what is given to them, and use it effectively. However, after beating Mom's Heart as the secret character, Isaac obtains The D6 as a starting item. The item allows Isaac to transform an item into another one, meaning Isaac can have a selection of 4 items per floor.
    • Cain/The Thief aka, Fragile Speedster: Cain is primarily luck based, with good damage and speed but low HP. His Luck Foot starting items makes him luckier than any other character in the game, and can turn a run around with one good pill or spin of the Gambling Machines. Cain's strength relies on getting lucky, and if it pays out, then Cain can become exceptionally strong.
    • Maggy/The Cleric aka, Stone Wall: Maggy has the most starting HP, but is slow and weak. To combat this, Maggy has a starting item (Yum Heart) that can restore a Red Heart every few rooms, keeping her HP high. She can also use this to enter curse rooms without losing health by regaining it using Yum Heart. Maggy's problems can also be taken care of if she gets a Devil item by sacrificing her high HP, meaning that Maggy can trounce the early game.
    • Judas/The Mage aka Squishy Wizard: Judas has low HP and good damage, but starts with the Book of Belial, which can boost his damage output to high levels, and is useful his whole run. If a Judas player can effectively make use of his offensive tactics, then Judas can be potentially the most powerful character in the game.
    • Eve/The Druid aka Critical Status Buff character: Eve starts with low HP and poor damage, but has Whore of Babylon, an item that boosts her speed, firing rate, and damage when she is at low health (which also activates at one full heart as opposed to half). Eve relies on this to be effective, and if she has a chance to obtain lots of spirit hearts and lower her red hearts, Eve can be a powerhouse that can trounce even the toughest of enemies.
    • Samson/The Berserker aka Glass Cannon (changed to a second Stone Wall in Rebirth): Samson has low starting HP and somewhat terrible stats, but begins with Bloody Lust, an item that increases his damage for every enemy that dies and resets when he leaves the room. Samson is bad against bosses, but in rooms with loads of enemies, he becomes a force to be reckoned with, able to blow through enemies with ease. Rebirth reverses his abilities, making him have as much starting HP as Isaac and become stronger as he takes damage rather than as he kills, so any items that provide healing can turn him into a powerhouse.
    • ???/Blue Baby/Lethal Joke Character: ??? has a distinct disadvantage to anyone else: he has no Heart Containers, only spirit hearts. While this may seem like an obvious downside, any and all effects that rely on having low HP automatically and permanently kick in, meaning that if he gains the right items (like Whore of Babylon), ??? can absolutely decimate any boss in the game, and sweep enemies to the side. Oh, and once you've unlocked the final levels, you are guaranteed to get your choice between two powerful low-HP items after defeating Mom. Besides this, Devil Rooms cost 3 spirit hearts for everything, and HP Ups only give you more spirit hearts. Rebirth also gives him slightly more damage and speed than Isaac (but not to nearly the extent of Cain or Judas).
    • Azazel/The Demon aka Glass Cannon / Fragile Speedster: Rebirth character. Starting with flying and a close-range laser, as well as the best starting speed, Azazel has to quickly switch between dodging fire and dealing in the pain up front. Starts with no hearts but three temporary black hearts, but unlike ???, can get new hearts.
    • Lazarus/The Paladin aka Master of None: Rebirth character. Lazarus starts with good health but otherwise terrible stats (including luck), but can revive with great stats but only one health. Pre-death Lazarus can't keep up with the other characters and post-death Lazarus is as fragile as Judas without the massive offense (and leaves you even worse off if it happens late in the run). The only way to make him really effective is to leverage his pre-death health to give his post-death self an advantage; either coast on it until you find a health up item and die on purpose, or go for broke by spending it all on devil deals.
    • Eden aka Luck Based Character: Rebirth character. The genderless Eden starts with randomly assigned stats and a couple of items. Since the number of times you can restart as Eden is limited, you have to make do with whatever the RNG gives you.
    • The Lost/Harder Than Hard: Rebirth character who starts with good items but dies in one hit and can never gain more health, ever. If you discover the complex sequence of events needed to unlock thisnote , you deserve your punishment.
    • Lilith/The Minion Master: Afterbirth character. Lilith is unique in that she starts blindfolded, which means she can't fire tears herself. However, her familiar Incubus copies her tears, which allows Lilith to still benefit from most tear-enhancing items. She starts with the Box of Friends, which creates an additional copy of all your familiars for the room, doubling her DPS (or more if you can find items that let you use the Box multiple times in one room) with Incubus alone, and even more with extra familiars. She also has the Cambion Conception which grants you a demonic familiar permanently after taking damage a significant amount of times.
    • Keeper/Mechanically Unusual Fighter: Afterbirth character. Unlocking him takes forever, so you would expect him to be overpowered, right? Nope. He uses Coins as Health, and all Hearts (as in every type of Hearts) automatically turn into Blue Flies. He also cannot increase his Max Health past 2 and all hits deal one full container worth of damage, effectively making him even more of a Two Hit Point Wonder than The Lost (who at least has flight to make dodging easier and (eventually) the Holy Mantle to absorb one hit per room). To top it all off, the Keeper's stats are all-around trash; he moves slow, fires slow, and has worse Luck than Lazarus. But to make things not completely terrible, he does come with a triple shot and you can unlock some profitable starting items for him.
  • Confusion Fu:
    • This is the basic niche of the Dead Sea Scrolls. It gives the effect of a random spacebar item per charge.
    • Any Rainbow item (including the 3 Dollar Bill) will have randomized tear effects that change every three seconds. The Pride Day Challenge in Afterbirth has you equip all of them at once, allowing them to stack with different random combinations.
    • The spider enemies from Wrath of the Lamb have quick and erratic movements. Their movements are impossible to read and thus are the bane of prospective No-Hit runs.
    • The Rainbow Baby has a random effect for every individual tear.
    • Eden in Rebirth starts with randomly generated stats and items.
  • Crapsaccharine World: Cutesy Thick-Line Animation, adorable characters... and the horrific monsters they have to beat to avoid becoming a red smear on the basement floor. Word of God says he did this intentionally to make the game more palatable.
  • Creepy Basement: Hoo, boy.
  • Critical Annoyance: Averted. The game alerts you that you have half of a red heart left by having the heart blink and by the character peeing themselves a little every time they enter a new room (except for Eve), but these aren't distracting. There are several items that activate when Isaac reaches critical status which alert the player as well.
  • Critical Existence Failure: Isaac is perfectly fine when at half a heart, besides peeing himself when entering a room. Dying causes him to explode into a mist of blood.
    • No longer the case in Rebirth, where Isaac will instead collapse to the floor as his ghost leaves his body.
  • Critical Status Buff: The Whore of Babylon item gives a major buff when you're reduced to half a red heart or have nothing but soul hearts.
  • Cursed with Awesome:
    • Literally with the Whore of Babylon item, noted above, which has the quote "What a whorrible night for a curse!"
    • Devil Rooms take your hearts and give you cool items in return.
    • Challenge Runs, introduced with Wrath of the Lamb, remove Treasure Rooms but give you a specific item set to start, which for some challenges can make the game a breeze.
    • Nine Lives. It immediately lowers your HP to one but gives you, well, nine lives; while you can gather spirit and black hearts to make up for it, those will be gone after you lose a life, which makes the whole lives thing pointless unless you're really skilled. However, it is insanely practical for the Lost, who cannot pick up any hearts and will always be at one HP regardless, which makes it a must-have for his runs.
  • Cybernetics Eat Your Soul: One of the items you can buy at the cost of heart containers in the Devil Room is Technology.
  • Cycle of Hurting: Respawning in exactly the wrong spot can result in your remaining Dead Cat lives being taken away by a Slide that you cannot avoid because of the Item Get pose.
  • Damn You, Muscle Memory: Regardless of whether you prefer W-A-S-D or the arrow keys to move, odds are you're going to trip up at least once from using both of them. Additionally, Q is "switch to your last-used item" in many games! but here it uses your pill or tarot card; E is "use item" or "interact with surroundings" most of the time, not drop a bomb where you're standing. The main problem with all this is that the game doesn't let you just re-bind the keys to something more comfortable.
    • If you use a controller to play the PC version, you'll quickly notice that the left trigger for using your special item is easy to mix up with the Vita version's left shoulder button that is used for dropping bombs; the special item button gets instead remapped to right shoulder button. Wait, why didn't my Book of Belial trigger? Oh cra- BOOOOOOOM!
  • Darker and Edgier: Compared to Meat Boy. And that's saying something.
  • Dark Is Not Evil: When you collect the Dark Bum, you get an ominous message saying that "he wants to take your life," which tends to have the player bracing themselves for a crippling Power Up Letdown. When he starts stealing red hearts from the ground if you don't pick them up fast enough, it's enough to make you wail in frustration... until you realize that for every couple of red hearts he picks up, he spits out a Soul Heart. This is almost always an excellent trade (especially if you're playing as ???, who has absolutely no use for red hearts), and it's enough to make you love Dark Bum more than Thomas Jefferson.
  • Dead Character Walking: It was patched out quickly, but there was a glitch in 1.3 that could do this. if you had only half a heart left aside from ???, who has no natural hearts, and take 1 heart of damage, rather than dying like normal, you would instead act as if you had constant mercy invincibility. It was as if you had Book of Shadows on constantly; touching or getting hit by Greed would still sap your money, but you never took damage at all, were counted at low health, and could use health taking machines, like the devil beggar or blood donation, constantly with no penalty, while technically dead. Picking up a full heart would restore you to half a natural heart.
  • Deal with the Devil: The Devil Rooms allow the player to exchange Max HP for items. Wrath of the Lamb introduces the demonic beggar, which damages the player in exchange for the possibility of dropping an item.
  • Death of a Thousand Cuts:
    • Maxing out tears in the early floors can result in this, depending on your base damage. Isaac with full tears and no damage upgrades can take down high level bosses such as Loki and Monstro II competently by swarming them with tears. Even more deadly with piercing, homing, or curving tears, or Standard Status Effects tears, whose effect chance is calculated on a per-hit basis.
    • The thin odd mushroom deliberately invokes this by increasing rate of fire greatly while reducing damage.
    • Technology 2 can be this, as it provides a near constant laser at the cost of 35% damage.
    • Rebirth has the Soy Milk item. It cuts your damage down to a measly 20% damage, but you can literally fire dozens of tears per second.
  • Degraded Boss: Many bosses can reappear somewhere as a "normal" enemy.
  • Denial of Diagonal Attack: While it is possible to influence the angle of your tears by moving strategically, other than that you'll have to make do with just the basic cardinal directions. Whipping shots becomes impossible with Technology and Spoon Bender, and similar items have no effect on it.
    • Subverted with the Marked item in Afterbirth, which lets you automatically fire tears in any direction.
    • Inverted with the "R U a Wizard?" pill effect and The Wiz item in Afterbirth, which make you fire tears diagonally, denying you from attacking horizontally and vertically.
  • Desperation Attack:
    • The Whore of Babylon item, which makes the player much stronger when having only half a red heart or only soul hearts. Eve starts the game with this item. It's not a Desperation Attack if ??? or The Lost picks up this item, as it is always active.
    • Wrath of the Lamb introduces a sort of desperation room, normally accessible only if the player has one heart remaining. These rooms always contain a special item... but they're also challenge rooms that spawn bosses when the item is taken. Again, ??? and The Lost can always enter these rooms. Unfortunately, these rooms were massively Nerfed in Rebirth, probably because they were easy to abuse. Items can still show up in these rooms, but it's more likely there will be a plain old chest.
  • Developers' Foresight:
    • Cain wears an eye patch. He shoots tears only from one eye, and when he acquires an item that would go over his patched eye, it's replaced with an exclusive-to-him version.
    • The Common Cold replaces your tears with poisonous mucus. If you find something that replaces your tears with something else (e.g. lasers), your attacks can still poison enemies, and most such items get an additional effect. Mom's Knife, for example, drips with green poison, and most lasers turn green.
    • The Black Candle item gives Isaac immunity to curses (i.e. negatives effects that affect your current floor occasionally). It also prevents you from being teleported by the Cursed Eye when you get hit. After all, it is cursed.
  • Difficult but Awesome:
    • Dr. Fetus allows you to shoot bombs instead of tears. On one hand, it can hurt you and it takes good timing. On the other hand, you have limitless bombs (enabling you to clear out rocks and get to items and secrets more easily), and enemies (especially bosses) die REALLY easily. This is taken Up to Eleven with the Ipecac Syrup in Wrath of the Lamb: Does more damage than bombs and poisons on hit, but its arcing path is very difficult to work with. And with Rebirth, the Pyromaniac item will heal you when you take explosive damage. It makes even Kamikaze worth picking up.
    • Eve has shades of this with her One-Winged Angel form accessible with one of her starter items (see Fragile Speedster/Glass Cannon below for more details).
    • Distant Admiration fly. With proper skills, it can kill a boss relatively quickly.
    • Mom's Knife. Incredible attack power, terrible range unless you charge it (and there's no indicator of how much you've charged it, so that's basically guesswork). Furthermore, since the knife does constant damage while in contact, the trick is throwing it so the target is at the apex of its flight, doing the most damage before it returns. Too much and it will graze them for less damage, while too little is none at all.
    • The Brimstone item. It upgrades your damage, can hit multiple times per shot, and ignores all terrain. On the other hand, it takes a couple seconds to charge up and it cannot be fired before it's fully charged. Moreover, it doesn't knock back enemies. However, anything which upgrades your tear fire rate shortens the charge time, and the Chocolate Milk item allows you to fire it without charging it up fully. It's powerful on its own on the early floors, but requires damage upgrades to remain useful later in the game.
      • The Wrath of the Lamb added Polyphemus, an item that lowers your fire rate and improves your damage significantly. Combined with Brimstone, it makes the laser shots charge even slower, but kill most bosses in one hit, and the final bosses in around 10.
      • The Gravity/Brimstone combo in Rebirth. Instead of leaving floating tears that eventually fire unless you release the attack key, it leaves behind timed Brimstone orbs that fire with the full force of a single Brimstone shot. While you have overall less control over your Brimstone, you can charge and fire it much faster since you don't need to wait for the first shot to run out before charging the next.
    • Diagonal-walking through spikes without taking damage. Requires practice, but mastering this little exploit is handy for getting free items that are otherwise inaccessible. Rebirth keeps this as an Ascended Glitch, though requiring slightly different timing.
    • The Keeper. He starts with triple shot (good), horrible speed, luck and rate of fire (bad), uses coins as health and cannot increase his max HP beyond two coins (horrible), which makes him a very difficult character to play as. However, you can eventually unlock the Wooden Penny (a one room recharge active item which has a 50% probability of spawning a coin upon use) as a starting item for him, which obviously acts as a healing item of sorts... But also lets you exploit the hell out of sacrifice rooms. In Afterbith, sacrifice rooms were revampednote , and they have a chance to either send you to the angel room, spawn an angel room item, or if you are very lucky, both. Which means that, if you find a sacrifice room in the first floor and leave a few coins laying around, it is possible to practically start the run with overpowered items such as the Sacred Heart or the Godhead (if you've unlocked it). Sacrifice rooms eventually spawn Angels, making getting the key to Mega Satan's room much easier.
  • Disc One Final Dungeon: The Depths 2, where you fight Mom. The Disc Two Final Dungeon, the Womb 2, was the original Very Definitely Final Dungeon, where you fight Mom's Heart/It Lives. A Halloween patch added Sheol, the new Disc Three Final Dungeon, where you fight Satan. Wrath of the Lamb introduces the Necropolis 2 as an alternate Disc One Final Dungeon, and Utero 2 as an alternate Disc Two Final Dungeon. It also introduces the XL versions of these levels, which combine stages 1 and 2. A later patch turns the Cathedral into an alternate Disc Three Final Dungeon, which has you fighting Isaac (a.k.a. yourself). Finally, with the Wrath of the Lamb version 1.3 patch, The Chest gets added as the Disc Four Final Dungeon, which has you fighting the Blue Baby as the final boss. Rebirth firmly turns it Up to Eleven with both a new, post-Sheol floor Chest equivalent called The Dark Room, with a new final boss, "The Lamb", as well as a secret final boss, "Mega-Satan".
  • Disc One Nuke: Due to the randomized nature of the game, it's completely possible to get powerful items like Brimstone or Epic Fetus on the first couple of floors.
  • Does This Remind You of Anything?: The whole game is one for Religion (specifically, the Christian faith). The game is populated with Christian iconography, and the plot itself is motivated by Isaac's mother supposedly receiving messages from God. The developer specifically stated that the game was inspired by the deep fears he acquired as a result of his religious upbringing.
  • Double Unlock: When you manage to unlock a secret item, you're only told it now has a chance to appear in the game. You still need to find it physically to use it!
  • Downer Ending: The first ending has Isaac about to suffer another murder attempt by his mother. Most subsequent endings imply Isaac was Driven to Suicide after his family fell apart and his mother started abusing him.
  • Down the Rabbit Hole: The trapdoor in Isaac's bedroom floor leads down to much more than a simple basement.
  • Dungeon Bypass: The "We Need to Go Deeper" shovel allows you to dig down to the next dungeon level without finding and beating the boss (and, if you're not judicious about using it, without picking up the powerups you'll eventually need to win the game). This can also be used to get to Sheol early.
  • Dummied Out:
    • The "Oh No!" / Explosive Diarrhea pill is probably one of the few unintentional examples, disappearing from the game sometime around the Wrath of the Lamb update. The pill returned not only in a patch to the original game, but also in Rebirth.
    • In Afterbirth, the first patch for it removed I.V. Bag from Greed Mode due to a possible unintended combo happening (I.V. Bag + Bloody Penny/Contract From Below/Piggy Bank/etc. with an endless supply of 3 cent red hearts from the shop = endless money). Too bad Eden didn't get the memo.
    • Afterbirth also has an unused boss known as "Skinless Hush", implied to be an alternative form of an existing boss. Both the boss' code and spritesheet are in the game's files, but the spritesheet has only one finished sprite and, if forced to spawn in-game, the boss has absolutely no AI attached to it. In reality, it was a Red Herring for data miners.
  • Dynamic Difficulty: Individual runs don't change depending on how well/poorly you do, but the game itself slowly changes the more times it's beaten, starting with unlocking more levels/bosses after Mom. After a while, more advanced versions of bosses replace their predecessors and other bosses change too, such as the 4 Horsemen of the Apocalypse appearing after Mom is beaten for the first time. Most notoriously, beating the game many times would steadily increase the chance that The Fallen would randomly replace a regular boss and would frequently appear on the first or second floors. On the other hand, unlocking more and more items with each completed run and experience with the game mechanics counteract this, keeping things more-or-less fair.
  • Early Bird Boss: The Fallen is unlocked as a random boss battle after beating the game for the first time. It is essentially a more dangerous version of Krampus that splits into 2 at low HP, giving you double trouble. Its presence is completely random and it can strike on the first two floors, often before you have any real means of killing it besides Death of a Thousand Cuts. If it shows up later, you're probably powerful enough to deal with it handily.
    • In Rebirth, The Fallen's HP is actually decreased on earlier floors, which makes things more fair.
  • Earn Your Bad Ending: The vanilla ending is pretty happy until it's revealed that it was All Just a Dream, and Mom's still coming for you. Most of the endings after that pretty much go downhill from there.
  • Earn Your Fun: More harder levels and gimmicky characters become unlocked and many of the more gamebreaking items in the game become available in the item pool once you beat the game in several ways, most ways being stupidly hard. Such as beating all the bosses on hard mode with only one hit point.
  • Eleventh Hour Superpower:
    • Level 4 Meat Boy, who can only be obtained without bug-exploitation just before the start of the last level of the game. The last level for your first ten playthroughs, at least... He will crush almost everything on that level with ease if you can stay out of the way for more than a few seconds.
    • You're guaranteed some of these in the the very last bonus level, The Chest, as long as you have keys — four golden chests are guaranteed in the starting room and every chest in the level has an item in it.
  • Elite Mooks: Each enemy type has a tougher, tinted / colored version that will almost always drop an item when killed. Different colors have different meanings, which are NOT consistent between enemies. An orange Knight won't act like Orange Chub. Bosses can also be colored as well.
    • The original game's Eternal Edition features even tougher white-colored enemies/bosses, which have several unique tweaks to their behavior that make them far more dangerous than usual. For example, the normally easy Monstro splits into two, then four smaller Monstros when he takes enough damage. Fortunately, these "Eternal" enemies only appear in the game's hard mode, and they are completely absent from Rebirth.
  • Enemies with Death: You get to fight Death, one of the Riders.
  • Enemy Roll Call: The ending shows the enemies crudely drawn on paper during the credits. Rebirth removed these, however.
  • The End... Or Is It?: Just as Isaac appears safe, his mother appears in the background behind him, holding a knife. One's doubt of final victory becomes apparent as all your victory means is that The Womb is unlocked and mother merely 'sleeps'...
  • Empty Room Until the Trap: Each level may have one specially marked room with a chest or item that, if you open/take it, will trigger three waves of enemies. Wrath of the Lamb offers a different version where you fight two degraded bosses in a row.
  • Everything Trying to Kill You
  • Evolving Weapon: The Cube of Meat, an item that only drops from The Harbinger bosses. Every cube you get increases how effective the powerup is. It also reminds one of a certain skinless boy after the second cube. Rebirth add the Ball of Bandages.
  • Evolving Title Screen: The title screen changes as you reach various milestones in the game, like killing the Final Boss or collecting every item.
  • Exploding Barrels: Wooden barrel variety.
  • Faux Horrific: At the beginning of each level, we see Isaac remembering some awful torture he has been through. In one memory, he is sitting on the toilet and notices there is no toilet paper left — but his horrified reaction is the same.
  • Feed It a Bomb: A useful strategy for dealing with Chub is to get it to charge you then drop a bomb in its path, causing it to eat it.
  • Flies Equals Evil: Flies are a very common enemy, and several other enemies vomit flies. You can even get in on the action with certain items.
  • Flip-Screen Scrolling: Not surprising for a game that takes cues from The Legend of Zelda. Although Rebirth adds some bigger rooms that use traditional scrolling.
  • Flunky Boss: A few bosses get their difficulty from swarming the player with enemies that act as meatshields at the very least. The Duke of Flies, the dark-shaded version of Gurdy, and Mom herself are the best examples.
  • Foreshadowing: While they usually just feature Isaac getting humiliated in some way, one of Isaac's between-level nightmares shows him suffocating inside of a chest, foreshadowing the Sheol ending and ???'s possible origins.
  • Freeze-Frame Bonus: Ending 13 has a hidden and hard-to-read message that appears for just an instant before it returns to the title screen. It reads "GET IN THE BOX!" (possibly a Shout-Out to Time Fcuk).
  • From Bad to Worse: One of the rewards is making the game more difficult after beating it a certain number of times.

    G-L 
  • Gainax Ending: At first. All endings after the "Epilogue" except the tenth, Endings 1-9, are little more than item/character/achievement unlocks with no plot-relevance, and make no sense within the story. However, Ending 10 is a huge Wham Episode, revealing that Isaac has been Dead All Along, as he actually suffocated to death in the Chest as seen in one of the vignettes, and Endings 11, 12, and 13 then explain the events leading up to that point, wrapping up the story.
  • Game-Breaking Bug:
    • One of the items introduced in the Halloween update, Brimstone, causes Isaac to shoot enormous streams of blood from his mouth. Sounds awesome? Depending on which upgrades you get or currently have, you may end up being unable to attack at all. The boss of the level added at the same time as Brimstone was also initially immune to it due to a bug.
    • Another glitch from the Halloween update: The Headless Horseman would sometimes replace the boss of the new level. This wouldn't crash the game, but this would horribly distort the music and you miss out on fighting the True Final Boss.
    • A similar glitch to the above used to happen in Wrath of the Lamb. The Random Event "Curse of the Labyrinth" combines two floors from the same tier into an "XL" version, causing the player to have to fight two bosses, one after the other. It is possible for the Final Boss to be the first boss fought in the Depths XL (or its alternate, the Necropolis XL). Normally, when the Final Boss is defeated, it becomes impossible to leave the room, and if the boss is fought first in the XL version, then the game would not recognize the level has been completed. This left the player stuck in an inescapable room, unless he can use a teleportation item. A similar thing could happen with Mom's Heart in the Womb/Utero. Thankfully, this bug was fixed a few days later.
    • Not exactly game breaking, but there's the whole mess with Wrath of the Lamb's True True Final Boss. The boss screen shows ???'s image with the name "Daddy Long Legs". Previously, it was an alternate version of Daddy Long Legs, labeled in the game's files as Triachnid (a Mythology Gag to a previous game by the programmer). Currently, it's Blue Baby. This created a lot of Epileptic Trees.
    • The v1.3 update had a severely exploitable one. Using a Blood Donation Machine or Demon Beggar to reduce your health to zero made you completely invincible until you picked up a heart. This made the No Damage Run achievements pathetically easy. Luckily, it was patched mere hours after the update.
    • The v1.03 update to Rebirth has a nasty one (that some people initially thought was an intentional change just to make the game harder). You can not bomb into special rooms (Treasure Room, Shop, Sacrifice Room, etc.) from Secret Rooms. This can lead to Unwinnable situations where you can use The Moon or Telepills to enter the Secret Room and find out that it only borders special rooms, giving you no way out.
  • "Get Back Here!" Boss: The second stage of The Mask Of Infamy (can only be hurt in the back, and it turns and zigzags very quickly). Also inverted with Lust and Super Lust, where you have to run away as fast as you can to avoid taking Collision Damage.
  • Ghost Butler: Every new room you enter with enemies in it will shut all the doors and won't let you leave until you defeat all the monsters within. Unless you have bombs, in this case you can blow doors open to force your way out. Although leaving rooms this way without eliminating every monster will respawn them all to their original numbers if you re-enter the room.
  • Glowing Eyes: Some powerups, such as Sacred Heart, cause this.
  • God Is Evil: Subverted. Guess Isaac's Mom was just a nutjob after all. Or manipulated by Satan. Or just like the biblical Binding of Isaac, it was a test of some sort. The question is who the test was for, but it's highly likely it was failed. Whether or not this was because Isaac's Mom was a nutjob or Isaac was either the anti-Christ or corrupted (as suggested by the ''Wrath of the Lamb'' ending) is anyone's guess.
    • Though if Ending 16 in Rebirth is any indication, Mom may have been making the right call...
  • Good Wings, Evil Wings: The Bible and the Holy Grail give you white wings. Lord of the Pit and any item giving you a demonic effect combined with Transcendence give you black wings.
  • Gorn: Most of the bosses and enemies are quite disgusting, along with several powerups.
  • Grossout Game: This one runs the full gamut: piss, poop, vomit, blood, Body Horror, fetuses, and so on...
  • Guide Dang It: There's no guide on how to unlock some of the special characters, several of which require at best counter-intuitive behavior. This was fixed in Rebirth, which details how to unlock them (and changes some of the conditions), while adding its own, even more obscure special unlock, detailed in that section.
    • Special items are items that make other special items show up less often if you pick them up. There is absolutely nowhere in the game this is told to you, and it took a long time before the Special stat was even discovered, and that led to all new strategies being used in order to get good special items. The Rebirth happened to change how they worked, as detailed in its section.
  • Guilt-Based Gaming: If you try to quit the game, Isaac will ask you "Are you sure you want me to die?"
  • Have a Nice Death
    Dear Diary, Today I died. I was killed by this thing [picture of monster] in some basement/cave/dark/warm/cold place. I leave all that I own [items] to my pet cat Guppy. Goodbye cruel world -XOXO Isaac/Maggy/Cain/Judas/Samson/Eve/Blue Baby aka ???/Azazel/Lazarus/The Lost/Lilith/Keeper
    • Although you can transform into Guppy, said character does not sign the death will.
  • Heart Container: These can be found here and there, although only one of them resembles a heart, and an anatomically correct one, in fact. Some even grant two Max HP, and/or restore all your health when you get them.
    • Eternal Hearts act as half a Soul Heart when you first pick them up (albeit sandwiched between your Heart Containers and your actual Soul Hearts on your HP gauge), but transform into full-on Heart Containers if you manage to hold onto them until the next floor (or pick up a second Eternal Heart).
  • Hearts Are Health: Your typical straight example, more or less copying The Legend of Zelda exactly. Notably, there's also the <3 item, which is a Heart Container that resembles an anatomical heart rather than a Heart Symbol.
  • Hitbox Dissonance:
    • The flies have a larger hitbox than their visible size. One one hand, this makes it easier to hit them. On the other hand, it makes it easier to misjudge how close you're allowed to get without getting hurt — not helped by their tendency to suddenly jerk towards you.
    • The Transcendence pickup removes your body, turning you into a floating head that can fly over rocks and pits. It does not, however, remove your body's hitbox. Getting hit even causes your body to briefly flash into view, just in case you were wondering why you were taking contact damage while hovering over that narrow crevice.
    • The tears hit box is their shadow, not the tear itself. This is normally a moot point, but bosses like Monstro can be a bit counter-intuitive without knowing this fact. It also makes Ipecac a learning experience, as the arcing tears will detonate despite logic suggesting they would said over obstacles or enemies. Knowing this makes the Suicide King challenge in Rebirth somewhat easier.
  • Hoist by His Own Petard: Several bosses have attacks that end up screwing themselves over, especially those with explosives. Bear in mind that no enemy is immune to their own blasts and you can take full advantage of that.
  • Holy Halo: With three different varieties! There's The Halo (which is exactly what it sounds like: a gold circle hovering above your head), there's Scapular (which is the older interpretation of the halo: a glowing light behind Isaac's head), and there's the Holy Grail (like the Scapular, it's a glowing light behind Isaac's head, but it's a "spikier" light. That is, it's a many-pointed star of light instead of a bright haze). Also inverted, in that there's three varieties of demon horns as well: Loki's Horns (tiny black horns Isaac wears on his head), the Pentagram (larger horns that literally grow out of his head), and Brimstone (giant, curled black ram's horns that sprout out the sides of his head).
  • Inexplicable Treasure Chests:
    • Treasure chests are everywhere in the basement of the house. Even more inexplicably in The Womb.
    • It's possible to unlock a treasure chest and find another smaller treasure chest inside, and although very rare, it's possible that chest has another still smaller chest inside it!
      • Which could happen while you're inside a chest!
  • Infinity+1 Sword:
    • Isaac's secret starting item. You need to beat the game's (initial) true final level ten times, which is quite a lengthy and dangerous task. And after that, you need to beat it once again with the resident Joke Character, which is nothing short of an extremely painful ordeal. But if you manage to accomplish this mission, your reward will be: The all-mighty D6 dice! An activated item capable of transmuting any collection related item(s) into other random item(s).
    • Another one shows up in the Halloween Update. Mom's Knife, which is absurdly powerful.
    • The D6 was arguably topped by the D20, which rerolls every type of item except for collection items (as Northernlion could attest to.)
      • Rebirth tops this with the D100. Will the chain ever end?
    • Rebirth adds plenty more unlockable, powerful items. But the big one has to be Godhead, which increases all tear-related stats, makes your tears homing, and gives them a damaging halo. It's unlocked by beating all the end-game bosses (except Mega Satan) and Boss Rush on Hard with The Lost.
      • Beating Mom's Heart on Hard with The Lost also unlocks the Infinity Plus One 2-Player Familiar. It's completely invincible.
      • Another example is the Stop Watch. It requires donating 999 coins to the shop, which, on average, requires two hundred playthroughs. However, while the unlocked-by-default Broken Watch only works at random (and sometimes it speeds up enemies instead), the Stop Watch is permanently active.
    • Afterbirth adds Mega Blast, earned by defeating Mega Satan with every character in the game. What does it do? It gives Isaac a fifteen second continuous blast of Mega Satan's blood laser that persists through rooms, floors, and has a twelve room charge time that batteries will only fill by 3. It will melt any boss in its way and the force behind it is so powerful it can force Isaac backwards.
  • Incredibly Lame Pun: "What a WHORRIBLE night for a curse!"
  • Interchangeable Antimatter Keys: In classic Zelda style, any key fits all locks, but disappears once used.
  • Interface Screw: Curse of the Lost disables your minimap, which can be a real pain if you get hit with it in the later levels which have dozens of rooms. Rebirth adds a Curse that hides the health bar.
  • Invincibility Power-Up: The My Little Unicorn and the single-use Chariot tarot card both protect from and cause Collision Damage. The Gamekid powerup turns the game into a short round of Pac-Man. The Book of Shadows prevents the player from taking damage.
  • Ironic Nursery Tune: After beating "It Lives!" for the first time, a distorted version of "Jesus Loves Me" replaces the normal credits music.
    • It's even creepier in the trailer for Rebirth
  • Item Get: Isaac will briefly hold up any upgrades, space-bar items, pills, and cards that he finds. This can be hazardous if he picks these up while there are enemies nearby...
  • Jack-of-All-Stats: Isaac starts as this.
  • Joke Character: ???, unlocked by beating the true form of the game's True Final Boss 10 times. He starts with the same stats as Isaac (not even Cain or Judas's improved offensive stats) except all his hearts are soul hearts, which can't be healed like regular hearts can. He can't earn regular hearts, either; any health upgrades are converted into soul hearts. He also starts the game with The Poop, which creates a pile of poop. His lack of heart containers prevent many items from doing anything.
    • Lethal Joke Character: The soul heart mechanic of the character does lend itself to some amusing exploits, though.
      • Devil/Angel rooms are guaranteed if you don't take red heart damage on a floor unless one recently appeared, in which case the probabilty is reduced. That means ??? always gets the maximum Devil/Angel rooms lady lucky is willing to give, no matter the amount of damage it took. The powerful items found in these rooms give ??? a significant edge.
      • Since Challenge Rooms check against regular hearts, he can enter them with any amount of health. The same goes for items which check against minimum health, meaning the Polaroid (temporary shield) and Whore of Babylon (Critical Status Buff) either activate every single time or are always on.
      • Items that grant a temporary health bonus instead grant a permanent soul heart (the Liberty Cap can thus be tediously abused for functionally limitless health).
      • The Wafer item reduces the cost of all Devil Room items to 1/2 a soul heart.
      • The Dark Bum turns into a tremendous help, since ??? has absolutely no use for red hearts pickups otherwise. Combine with the Bloody Penny and you'll have a constant stream of health reserves.
    • In Rebirth, there's an even larger Joke Character in The Lost. While playing as The Lost, you start with no health and cannot pick up any health, meaning that you will always die in one hit, meaning you'll need a no damage run to win. You don't even start with anything particularly unique - you can fly, but so can the other character with Brimstone and actual health. The only thing he has going for him is He gets items in devil deals for free. Though, mercifully, he now has some bonuses, due to an update that launched the same day as Afterbirth, in the form of Spectral Tears and the D4, allowing The Lost to re-roll his build...but this is offset by the fact that you can also start with the Holy Mantle after donating enough coins through Greed Mode. Now the player has to choose to keep what precious little protection The Lost can have, or use the D4, re-roll your entire run, and risk it all.
  • Joke Item: The Poop, which just drops a pile of dung where you're standing and can be used once per room. Maybe it can be used for cover and maybe it can be used to block an enemy chasing you, but virtually any other item is more useful in any situation.
    • In Rebirth, there is a synergy that turns The Poop into an outright fantastic item. Combining it with Midas' Touch means that you'll be able to drop golden poop every single room!
  • Jump Scare: One of the bosses, Polycephalus. Besides its appearance, whenever it digs down it reappears with a unique scream.
  • Kaizo Trap: Due to the way Mom's attacks work, you can still be hit when you kill her. Her foot is preceded by a shadow, and if she dies while the shadow is present, the attack hits that spot instantly.
    • When Mom's Heart/It Lives is defeated, it releases a circle of blood shots. They aren't unavoidable or anything, but a distracted player can be damaged or even killed if not careful.
  • King Mook: Chub is the standout, but as of Wrath of the Lamb, the Mask of Infamy is for the Mask-Heart enemies.
  • The Krampus: Added as a boss in the Christmas update. The Krampus will randomly appear in the Devil Room (10% chance at first and 40% at later visits) and drop one of two unique items when defeated.
  • Last Ditch Move:
    • Some enemies explode, while some others spawn bullets when killed. For bosses, Steven has a last-ditch move.
    • The Daddy Long Legs tries to crush you with its body as it dies.
    • Due to a glitch, sometimes the effect of final bosses dying can actually hurt you.
  • Last Lousy Point: Obtaining Platinum God (and, in Rebirth, Real Platinum God) requires touching every item in the game at least once. Some of these items, such as Sacred Heart, are so rare and are tucked away in areas that are so rarely accessed that it can take forever to find that last lousy item without some form of infinite rerolls. Rebirth adds some other items into the mix, such as every Secret Room exclusive item (Skeleton Key and Black Lotus are two) due to the fact that Secret Rooms rarely contain items anymore. Perhaps most infamous is Steven, which has been removed from every item pool, meaning it's only attainable as a rare boss drop from Steven himself and cannot be rerolled from Little Steven.
  • The Legions of Hell: Isaac has to fight a number of demons during the course of his descent through the basement, usually as bosses. One of the unlockable characters, Azazel, is a demon himself.
  • Lethal Joke Item:
    • The Bible grants flight for a room and doesn't recharge for another six (barring other items to increase charge time), but kills the final boss and the original two True Final Bosses in one use. Don't try to use it on any of the True Final Bosses added after the initial release, though. Just don't.
    • By extension, the Rosary has a fairly disappointing obvious effect (It just adds three soul hearts), but it can often be used to cheat the devil out of some of his nicer items without dying and has the side effect of making a Bible more likely in shops, guaranteeing an easy final boss if you get it. Plus, when playing as ???, it's a godsend.
    • The Dead Cat item makes it so you gain eight extra lives, at the cost of setting your max HP to one when you pick up the item and whenever you die. Normally this is a pretty lousy trade-off, but if you only have one heart at the time or are playing as certain characters (Judas, Samson, or especially ??? and The Lost), it's basically free lives.
  • Light Is Not Good: Cathedral is unusually bright for a Binding of Isaac area, but it's just as likely to kill you as any other area in the game, if not more so.
  • Living Apart: In later levels, enemies are encountered that are just living brains, rolling guts, or disembodied hearts.
  • Logic Bomb: In Ending 6, Mom's fist flies out of a chest that was spawned by destroying her heart, which was inside her womb, which was inside her corpse in the first place. So Mom was hiding in a chest in her heart in her womb inside her to begin with. Yeah. Figure that out.
  • Losing Your Head:
    • Some of the enemies can attack the player even after losing their body or head or they just get separated.
    • Transcendence removes the player's body, allowing you to float over rocks, pits, spikes, and damaging liquids. One of the better items.
    • The Shears and the "The Hanged Man" Tarot card also do this, but only for one room. Transcendence, a noose, does it permanently. If Isaac has items that make him look demonic, on the other hand, he gets wings instead.
    • The Guillotine from Rebirth turns Isaac's head into a familiar. If you can get past the Interface Screw, the head not only protects the body from bullets but the item is also a stat boost.
  • Luck-Based Mission:
    • Every single playthrough, due to the randomized nature of the game. You can never guess if items will complement each other, or if they'll even be useful. This includes boss drops and shop inventory. Key and bomb drops can either leave you with a surplus or lock you out of chests and treasure rooms if you fall short. The good stuff in the shop costs just enough that you probably won't be able to pay for it until you've gone down three or four levels, when Greed loves to lay its ambushes. Pills are always random, and are just as often bad as good (unless you have the Lucky Foot or PhD). Slot machines and the like won't pay out half the time without good luck. Basically, there is always a chance that you will reach the end of the game with a much more or less powered up character than you expected through no fault of your own. On the extreme, it's possible to get absolutely no useful upgrades, all bonuses being activated items that you do not want, or things your character doesn't benefit from at all. On the other hand, it's possible to get an item combination that absolutely dominates everything. That said, due to the way items are unlocked, each successful playthrough means it is more likely items will be useful, and the fact that the game gets longer means more items to find. The first playthrough is often the toughest.
    • Acquiring 4 Cubes of Meat! It requires you to fight and kill all four Harbingers in a single playthrough. Unfortunately, they don't usually all show up on the same run. Acquiring the Book of Revelations early on almost guarantees fighting all four of them, but finding it early enough is another luck mission on itself. Also, it's not even a complete guarantee - even with the Book of Revelations, Conquest can replace Death on the Womb/Utero and give you the White Pony instead of a Cube of Meat. In Rebirth, it's even worse - the Harbingers now have an equal chance of dropping either a Cube or a Ball of Bandages, and there's a separate achievement and reward for getting four Balls!
    • Bosses also contribute to the luck-based nature of the game. Not all of them are equally difficult, and depending on a character you choose and powerups you get, some might be a cake-walk (Larry Jr., Loki, etc.) and some an endless source of frustration (Gurdy for a slow-moving character, Monstro II for people who dislike close-range combat, or The Bloat for pretty much everyone). And since not getting hit (which is more difficult if you get a boss you are faring poorly against) is almost a requirement for getting access to the devil room, which often allows one to balance the odds, the difficulty snowballs depending on how much the Random Number God loves (or hates) you.
    • There's also no way to tell if a shop or a secret room will spawn Greed/Super Greed instead.
  • Luck Manipulation Mechanic:
    • The dice items allow the player to reroll various facets of the game. In the original, the player could reroll permanent items (D6) or pickups (D20). Rebirth adds the ability to reroll enemies, the player's own items, and everything at once.
    • The Book of Belial guarantees a Devil Room/Angel Room on that floor, provided that floor meets the conditions for spawning one (it won't work on the first floor or past the Womb). Rebirth adds the Goat Head, which is a permanent item with the same effect.
    • The Book of Revelations also ups the chance of the player encountering one of the Harbingers (and acquiring a Cube of Meat in the process) in the Boss Room, with repeated use on that floor making it all but guaranteed. The Headless Horseman and Conquest can still screw up an attempt to construct Meat Boy, though.
  • Luck Stat: It starts at 0 and only affects two things: the chance of getting a drop after clearing a room and the chance of firing special effect tears (for example, shooting a tooth with the Tough Love item). Somewhat ironically, negative luck actually increases the former in most cases. While the Lucky Foot item and Lucky Toe trinket both increase the chance of getting a drop after clearing a room, they do not actually increase the Luck stat.
    • Luck has been fixed in Rebirth. Lucky Foot and Lucky Toe actually affect the Luck stat, and Luck now affects certain items and slot machines.
  • Ludicrous Gibs: The fate of every single enemy you destroy is being turned into these. The only exceptions are Isaac, ???, and Afterbirth's Little Horn.

    M-R 
  • Macrogame: Each playthrough is different than the previous one, but as achievements are unlocked, more and better items begin appearing.
  • Magikarp Power:
    • In terms of items, the Wafer makes anything that hurts you do exactly one half-heart of damage. It does almost nothing for the first half of the game (where pretty much only Champion enemies, collision with bosses, and your own bombs hurts for more than that), but starting at the Womb, everything does a full heart of damage, so the wafer effectively doubles your health (and any health pickups).
    • Using Guppy's Paw (which trades heart containers for three soul hearts each) isn't so good at the start of the game since red hearts with which to fill your heart containers are easy to come by, unlike spirit hearts. However, using it later in the game is benefecial as both are scarce and functionally similar. Spending all of your heart containers will give you three times your max health, whether your heart containers are empty or not. Additionally, doing so will give you all benefits of the Lethal Joke Character.
    • Believe it or not, ???. Mom always drops The Polaroid when killed. Besides being required to access the Disc Two Final Dungeon, the Polaroid casts a protective shield wherever you have 1/2 heart or less. ??? always has 1/2 heart or less. That's right folks, the Lethal Joke Character has the greatest life expectancy in the late game.
    • The Bible. It allows you to fly for a single room. While useful, there are items that grant this effect permanently and don't take up your special item slot. It also has the slowest recharge rate possible, so you only get flight once every six rooms (without upgrades). But, if you use it on Mom and Mom's Heart/It Lives, they die instantly, allowing you to bypass two of the hardest bosses in the game and making the No Damage Run in each section a lot easier. Just don't use it on the final bosses.
    • The Cube of Meat (and Ball of Bandages) start as this. Their familiars help with blocking hits and damaging enemies, but are otherwise unremarkable for a boss fight reward (specifically the Harbingers). With each Harbinger defeated, though, the Cubes or Balls slowly takes form as the more useful Meat Boy (or Bandage Girl if you collect the Balls). Level 4 Meat Boy/Bandage Girl is especially powerful; the hard part is somehow assembling one and getting substantial use out of them, since finding 4 Harbingers that drop the same pickup isn't that likely to happen without holding onto the Book of Revelation for several levels.
  • Malevolent Architecture: Useful items may be stuck behind rocks or pits, and in many cases it's not worth expending a bomb to get to them. In later levels, this gets more and more common, in addition to rooms being laid out to make attacking enemies more difficult (and them attacking you easier) and eventually adding random spikes.
  • Marathon Boss:
    • If your damage output doesn't scale as you progress through the game, later bosses can take an obscene amount of effort to kill. This is especially true of Isaac and ???. And then there's Mega Satan of Rebirth, who takes forever without the Chaos Card due to being a Boss Rush as well as a regular boss.
    • Afterbirth adds in Hush and Ultra Greed, who are unique in that their HP is scaled so you won't wind up with a combo that can kill them in twenty seconds. No matter how well-prepared you are, expect to spend a lot of time killing them.
  • Meaningful Name: The Wrath of the Lamb expansion's name foreshadows two of the bosses introduced in the game (i.e., a Messianic Archetype version of our main character, and one of his alter egos).
    • The titular Lamb itself makes an appearance in Rebirth, if you bring the Negative down to Sheol. You are taken to the Dark Room area, where you'll have to fight the Lamb
  • Memento MacGuffin: The Polaroid, which depicts Isaac's family before the madness started. Getting knocked to half a heart with it on gives Isaac a protective shield. Defeating the Cathedral's True Final Boss while holding it takes you to the Chest, where you fight the Blue Baby. Rebirth adds it's counterpart, an unrecognizable picture of Isaac's family called The Negative. Instead of a shield, it deals damage to all enemies when Isaac is brought to half a heart, and upon beating Sheol it brings Isaac down to the Dark Room to fight the Lamb.
  • Mood Dissonance: The Arcade rooms are very nicely furnished and bright, with a very chipper 8 bit remix of the first level theme. It's a bizarre contrast to the rest of the game.
  • Mook Maker: Several of the bosses, though not all of them. Also one of the enemy types. It Lives is a Degraded Boss Maker.
  • Money for Nothing: Once you reach the Womb, money has very little use, as there are no shops to be found anywhere in there.
    • Subverted if you happen to get the Money=Power upgrade, which is does Exactly What It Says on the Tin, increasing your attack power in direct proportion to the number of coins you have. Also, you can still find beggars, slot machines and even arcades in The Womb to dump off your hard-earned gold in exchange for hearts, items and keys.
  • Mythology Gag: Several of the bosses and items are references to other works by Edmund. Namely, the Cubes of Meat, Dr. Fetus and Mega Fetus, the Super Bandage, Larry Jr., C.H.A.D., Steven and Li'l Steven, blobs that look like Gish, Gish himself as a boss, and Triachnid in Wrath of the Lamb.
  • Multiple Endings:
    • Depths Ending: Isaac is saved from Mom when a Bible drops on her head. However, this is then revealed to have all been a story Isaac was drawing. The real Mom proceeds to break into Isaac's room holding the knife she wants to use to murder him.
    • Womb Endings: Isaac opens a chest to find various items inside, culminating with what appears to be his own rotting corpse.
    • Cathedral Ending: Isaac looks in the mirror and realizes he is corrupted with sin. He then looks at his toy chest.
    • Sheol Ending: Isaac's Split Personalities, ending with a demonic looking one, flash before him. Isaac decides to climb into the toy chest in his room, possibly to kill himself.
    • Chest Ending: The collapse of Isaac's family is shown through a series of Polaroid photos. It is implied Isaac may have killed his sister by locking her in his toy chest, causing his father to leave and his mother to start abusing him.
    • Dark Room Ending: Isaac's mother is shown wandering outside, searching for the now missing Isaac.
    • Golden Door Ending: Isaac is shown after locking himself in his toy chest, flashing in and out of a demonic, grinning self-image, ending with him permanently staying as a demon.
    • Blue Womb Ending: Isaac's mother discovers Isaac's remains in his toy chest, before cutting to Isaac waking up in the underworld, with a shadowy, demon-like figure looming over him.
    • Greed Mode Ending: Isaac is trapped in a cave-in, and hangs himself shortly after. It then shows a Shopkeeper in the same room, who cracks a grin after a moment, implying that Isaac has become another Greed.
  • Mundane Made Awesome: After everything that just happened, Isaac gets rather surprisingly excited over the items in the endgame chest, including a hat, a nail, a quarter, a fetus in a jar, a wafer, and some bling.
  • My Name Is ???
    • The last unlockable character is simply called "???". Fans have nicknamed him "Blue Baby".
    • The Blue Womb is named "???" when you enter the area.
  • Name of Cain: One of the unlockable characters, not surprisingly considering all of them have Biblical names. While not outright evil, Cain is somewhat shady-seeming — he wears an Eyepatch of Power and his abilities make him resemble a "rogue" class.
  • Night of the Living Mooks: There are various undead enemies Isaac must defeat. See also Non-Human Undead, below.
  • Nintendo Hard: Much like the Roguelikes it's based on, Isaac has no continues. You start with one life and additional lives are very, very unlikely to show up once along multiple playthroughs, much less a single one. If you die, you start all over again. The configurations of rooms and upgrades are randomized, and in some situations damage will be unavoidable. Survival depends on reflexes and calculated risk.

    And Wrath of the Lamb takes this even further! If you thought the vanilla version was merciless, you won't survive the new horrors you'll face here.
  • No Cutscene Inventory Inertia: No matter what the player has picked up, the character at the cutscenes is still what he was at the beginning. For that matter, it'll still be Isaac no matter which character you're playing as. Although, considering the achievements imply most of the characters are Isaac wearing a Paper-Thin Disguise of some sort, it may be fitting after all. The only exception to this is Lazarus, who will be crying blood after he's resurrected.
  • No Damage Run:
    • A no damage run of each area will earn you a Steam Achievement.
    • The Devil/Angel Rooms can only be accessed by playing through a level without taking any red heart damage and no damage at all against the boss. The exception is Basement II, in which the Devil Room is guaranteed so long as you don't take red heart damage.
    • Enforced with The Lost, who literally has no health and dies if hit by anything.
  • No Ending: If the player has gotten all of the Womb endings, then going to the chest when it appears again (such as during Challenge runs) will just take the player straight to the end credits.
  • No Ontological Inertia: Averted; any flunkies spawned by a boss will not die when the boss does (except in the case of Mom) and must be killed in order to clear the boss room.
  • Non-Human Undead: Remember those horrific monsters Isaac must defeat? They come back from the dead later.
  • Non-Indicative Difficulty: The "Challenges" stick you with various item loadouts and usually don't allow treasure rooms. Depending on the loadout, the game can either be hilariously easy or unspeakably difficult.
  • Obvious Beta:
  • Offing the Offspring: Unsurprisingly, since the game was named after the original (the Choice of Abraham kind).
  • Old Media Are Evil: The plot and imagery are inspired from inflammatory Christian propaganda from The '80s, such as the Jack Chick comics.
  • Ominous Latin Chanting:
    • "Enmity of the Dark Lord", the song that plays when you fight Satan and "Lament of the Angel", the Cathedral's background music generate this impression using gibberish. "Everlasting Hymn", Rebirth's Cathedral music, has real Latin, as does Ascension, the music that plays during the Blue Baby fight.
  • One-Hit-Point Wonder:
    • If you take a Devil Room item without having the regular hearts to pay for it, but still have soul hearts when you do, Isaac is reduced to zero health (no hearts or soul hearts) and will die from a single hit. Any health upgrades you collect instead pay off the debt, after which they can be acquired normally. You can, however, collect more soul hearts for a buffer. Rebirth altered this so you only lose your red hearts, keeping soul and black hearts.
    • The Lost lives off this trope, literally starting with no health and incapable of increasing it. Hope you brought your Holy Mantle.
  • Otherworldly and Sexually Ambiguous: The multiform Eden is neither male nor female.
  • Ouija Board: Serves as a power-up that gives Isaac ghost tears that move through objects.
  • Palette Swap: Enemies with a different color palette. They're stronger but drop items upon death.
  • Paper-Thin Disguise: It's heavily implied that the unlockable characters are just Isaac wearing these.
  • Photo Montage: The 13th Ending shows various Polaroids of Isaac and his family's life before the events of the game.
  • Plunger Detonator: The Remote Detonator item.
  • Potty Failure: The item "Lemon Mishap" allows you to lay down a puddle of pee that damages enemies, and the item "Number One" replaces your tears with a rapid-fire stream of urine. Also, certain pills will give you bad gas or literally explosive diarrhea. There's also the boss monster Peep, who uses urine as his main weapon.
  • Pun:
    • For example, a certain pill makes Isaac shit bombs note .
    • The Skeleton Key, an item which gives you 99 keys (the maximum and more than you'll ever need) has a skull for a handle.
    • A lucky foot usually belonged to a rabbit before becoming lucky - not so in the case of the Lucky Foot item.
  • Power-Up Letdown:
    • The Lost Contact can serve as this, situationally. It makes your shots intercept regular enemy projectiles, destroying both. In many cases, this is good. However, if your rate of fire is too low, and/or the enemy's is too high, it can make it incredibly hard to land a hit. The fact your shots block enemy shots effectively means that enemy shots can now block yours. Certain extremely fast-firing enemies can simply bore through your attacks and continue to hit you with impunity while preventing you from striking back.
    • The Tick, a randomly spawning trinket that makes bosses start out at anywhere from 5 to 15% less health from full, is fairly useful. What makes it bad is that it latches onto you and can't be removed by anything, making the negatives of it far outweigh the positives, and since the the Polaroid is needed to reach The Chest, picking the Tick up by accident when you can't find or buy mom's purse basically makes the game Unwinnable by Design. Luckily, Rebirth Ret Cons the Polaroid - and it's new counterpart the Negative - into permanent powerups, allowing the Tick and the Photos to exist in harmony. It even buffs the Tick with a health-recovering effect.
    • Despite being considered by the game as an upgrade, Shot Speed is generally regarded as nothing but a negative due to making it harder to lead shots to hit at diagonals, zero synergy with any item in the game, and actively detrimental to items like homing tears (tears have a limited turning radius; the slower the tears are, the sharper the turns they can make) and Lump of Coal (Lo C tears get stronger the longer they're in the air. Faster tears hit a wall, an enemy, or the ground faster, thus limiting the amount of damage they can build). Many players actively skip shot speed ups, only possibly taking Stem Cells (which has an HP upgrade attached to it) or Cat-o-Nine-Tails (which has a damage upgrade attached to it).
    • A high speed stat, as well. You'd think it'd be useful, but once you get four or five, it becomes very difficult to control the character and prevent yourself from careening into spikes, monsters, fires, shots, etc. Less obvious/problematic with flight. High speed can also make it very difficult to aim tears while moving.
    • Any item that either conflicts severely with items you already have (Mom's Knife after finding a Fetus item, for example), do not benefit your character at all (Yum Hearts for ???, anyone?), or is an activated item found after finding your activated item of choice.
    • My Reflection, which turns all your shots into boomerangs that follow you. These have abysmal range (and any range pickups you get make them boomerang further, which is pretty much useless) and behave in goofy ways which can be hard to predict or keep track of because they follow you rather than a trajectory. They could theoretically be useful, but you'll probably just get hit more by having to think about them.
    • Collecting Number One or the thin Odd Mushroom after already collecting many fire rate upgrades. Both of these items are extreme increases to fire rate at the cost of range or damage, but if you've already got a high fire rate...
    • The Dead Cat item. You have eight extra lives, yes. You also have your health bar reduced to one heart (and any health bar increases you find vanish on respawn), and if you die you respawn outside (with your secondary item still used up if you used it and any Soul Hearts still gone) and enemies fully heal. Good luck beating any bosses you couldn't kill on the first try. And those eight extra lives are going to need to last you the entire rest of the game.
    • The Coin Purse. Its only effect is an automatic four pill spawns. Nothing says those pills have to be good. For every time you get four stat-up pills, there are at least three when you get a net stat down or else it's a wash, and you can't tell which you've got unless you've found the PhD pickup, or be able to only get good effects with Virgo.
    • Sacrifice Rooms usually aren't worth the effort - at most, you'll get a Chest.
    • Spelunker. Yay, you can find secret rooms automatically! But you still have to bomb them open, and the X-Ray Glasses do the exact same thing except they also open the room for you.
    • Lord of the Pit, which grants flying and a minor speed boost. It can be found in a Devil Room and costs just as much as Spirit of the Night, which grants flying and spectral tears, the latter far more useful than the speed boost in almost all cases.
    • Level 3 and 4 Meat Boy might be seen as this depending on your situation. On the other hand, you get another familiar that deals contact damage and homes in on enemies, meaning later bosses like Isaac and ??? take damage faster since they never move, allowing Meat Boy to camp over them the entire fight. On the other hand, the two bosses also utilize Bullet Hell tactics, so having that extra orbital to block shots with might be more important.
  • Purposely Overpowered: The Wrath of the Lamb expansion adds a lot of incredibly powerful new items and effects that would be extremely abusive on the vanilla version of the game;note  You'll need every one of them if you want a chance to survive (not win, just survive!) the horrors you'll find on the new floors.
    • Samson in Wrath of the Lamb, who is basically Judas with a slightly lower base attack. (He is skilled at fighting mobs of enemies, but that's not much consolation if you have to fight one of the few bosses that doesn't summon punching bags.) He is rebalanced and further differentiated from Judas in Rebirth.
    • Guppy. While the ability to fly and spawn blue flies is pretty good, it requires a three item combo; one of these may need to be the above-mentioned Dead Cat, and you'll almost definitely need to trade in some health in a Devil Room for it. In comparison, the three item combo of Wafer+Habit+Yum Heart/Book of Revelations/The Nail makes you functionally invincible for the entire game, and there are two item combos that are significantly more powerful than Guppy.
    • The Stop Watch in Rebirth. It takes forever to unlock, but it gives all enemies and their bullets the slowdown effect. For the rest of the run.
    • Mega Blast in Afterbirth. It too can take forever to unlock, but it's a massive Brimstone laser which has insane damage and persists between rooms. It has the honor of being the only item in the entire game with a 12-room charge.
  • Powerup Magnet: There's a "Magneto" powerup which attracts powerups even through rocks and over gaps.
  • The Power of Love: The Polaroid, a picture of what seems to be Isaac and family, shields Isaac on his last hit point.
    • The Power of Hate: Rebirth adds The Negative, which is The Polaroid's dark counterpart. It damages all enemies when Isaac reaches his last hit point.
  • Psychopathic Manchild: Several bosses give this impression due to the goofy, yet deranged smiles they make when attacking.
  • Quirky Miniboss Squad: The Seven Deadly Sins are this, each one a personification of its namesake.
  • Random Event: The Curses introduced in Wrath of the Lamb, which are randomly activated at the beginning of a level. Curse of Darkness makes the map useless, while Curse of the Lost increases the size of a floor from what it would normally be and removes the pattern for Secret Room spawning. Curse of the Labyrinth combines two floors of the same tier—including two item rooms and two bosses.
    • Rebirth changes the Curses around and adds some new ones.
  • Recursive Ammo: The Parasite gives Isaac the ability to split his shots when they hit something.
  • Reset Button: Forget Me Now, an item unlocked by defeating Satan with ???. It starts you over from the beginning of the current level with a new layout and new monsters, including the boss. Why would you want to use this? The reset level also has new items, giving you more opportunities to power up your character. The only problem is that Forget Me Now is a one time use spacebar item, forcing you to abandon your current spacebar item and beginning the reset level with that item slot empty.
    • One of Rebirth's Dice Rooms has the same effect as Forget Me Now.
  • Revive Kills Zombie: The Bible, while normally dealing no damage, kills Mom and Mom's Heart instantly. Inverted with Satan, Isaac, and ???; using the Bible will instantly kill you instead.
  • Rewarding Vandalism: Rarely, destroying poop and putting out fires drops an item. Rocks with a small X on them (usually identifiable by their blue-tinted color) will also drop an item when bombed. (Destroying lots of poop this way unlocks The Bean, and blowing up enough rocks unlocks The Small Rock.) And then there's the secret rooms, which are revealed by blowing up walls.
  • Roguelike: Things like level layouts, monsters, items, and most bosses are randomly generated — though it's also level dependent (i.e. you will never find a Caves boss in the Basement, unless the boss could appear in both). Wrath of the Lamb even randomizes what level you'll be sent to by providing alternate stages. For example, in the original version, the first two levels would always be the Basement. After the expansion, each of the first two levels will be either the Basement or the Cellar.
  • Rummage Sale Reject: Given that every passive item picked up includes a cosmetic change to go with it and that these visuals stack graphically as you collect more items, Isaac's appearance by the end of your run is guaranteed to look like this in normal play... when it's not just straight-up Body Horror.

    S-Z 
  • Save Scumming: Because the game is randomized, you can instead do this on startup to get preferential powerups instead of garbage (the latter being more likely).
  • Scare Chord: Played on certain endings and when you enter the Devil Room.
  • Secret Character: ???, who is actually Dead Baby from one of Edmund Mcmillen's earlier works.
  • Self-Deprecation: The creators of the game appear as a rare variant of one of the Seven Deadly Sins. Namely, the the butt-ugly Ultra Pride, due to a feeling of pride and satisfaction at finishing their game.
  • Self-Imposed Challenge: Pretty much the only reason why anyone would pick up the nine lives item (which reduces your hearts to only one and resets them to one every time you die) willingly outside of 100% Completion, the challenge of the same name, or turning one of the characters into Guppy.
    • The Challenge Runs in Rebirth are now even more challenging! Well, some of them. "Computer Savvy" gives you Technology 1 and Technology 2 right at the beginning (but no Item Rooms), so that's fairly easy, but challenges like "Beans!" or "Solar System" prevent you from firing any tears at all (rendering some pills, some tarot cards, and almost half of the game's items completely useless), forcing you to kill everything solely with specially-powered poop-bombs or orbiting attack-fly familiars.
  • Sequential Bosses: Particularly the True Final Bosses. Special mention to Satan, the only boss with multiple health bars. Rebirth tops Satan with Mega Satan, who, including all of the Degraded Bosses he summons, has twelve separate phases.
  • Sequence Breaking:
    • It's possible to reach Sheol without beating the game ten times either by using the "We Need To Go Deeper" item or taking the hatch in the (possible) Devil Room in the supposedly last stage. Rebirth allows you to use Angel Rooms to reach the Cathedral.
    • While it might be a bug, it's currently possible to get credit for beating the game as ??? long before you can even unlock him...by using The Ankh, an item that gives you an extra life, at the cost of transforming into ??? on respawn. Considering you can't unlock the character until you've beaten the (constantly growing and changing) game 10 times, finding this particular item, and getting to the final boss, and then dying to respawn can save you a LOT of time and trouble, as you keep most other powerups when you come back... meaning you don't have to play a full game with what is essentially a joke character to unlock a powerful item for Isaac.
  • Serial Escalation: This game has issues with one-upping its own final dungeons every couple of patches.
  • Set Bonus: As noted in Ascended Extra, acquiring 3 out of 4 specific cat-related itemsnote  in a single playthrough will transform Isaac into his deceased cat, Guppy. Not only does it make you look hilarious / adorable, but it grants you the abilities to fly and spawn blue flies whenever you hit enemies.
    • Rebirth adds a few more cat-themed items, and also adds a new transformation, the Lord of the Flies. It's a bit of a letdown, though.
    • Afterbirth adds even MORE transformations, including Mom (grants you a Mom's Knife familiar) and an Angel (flight plus some soul hearts).
    • The Eternal Edition of the original game adds an angel transformation if you get seven health upgrades from eternal hearts in one run.
  • Seven Deadly Sins: Personifications of these are present in this game as minibosses. Beating all seven unlocks a new item. Super versions appear in Wrath of the Lamb.
  • Smart Bomb: The Death tarot card, the Necronomicon, and one of the functions of the Sun tarot card.
  • Shout-Out: See ShoutOut.The Binding Of Isaac.
  • Skeleton Key: Gives 99 regular keys, which is probably all you'll need and then some. In Wrath of the Lamb, the Golden Key allows you to open any door in the floor where you get it without spending any of your Interchangeable Antimatter Keys, then vanishes after the floor is exited.
    • A variation of this is the Dad's Key active item: Upon using it, every single door in the room is unlocked. Every single one. Even the door to Mega Satan in Rebirth.
  • Sorting Algorithm of Weapon Effectiveness: For the most part, items unlocked later aren't any more powerful than those at the beginning... except the familiars, where the ones available at the start fire vanilla bullets and those acquired later have much more exotic and useful attacks. And the health-increasing items, where the unlockable ones generally either heal you or give you some soul hearts as a bonus.
  • Spikes of Doom: These appear in later levels in some of the rooms.
  • Spiteful A.I.: Some players say that the game has a "troll engine" that manipulates the random drops you get just to laugh in your face, especially if you tempt fate by grumbling about never having enough money for shops, and then the game gives you a Steam Sale (half-off everything in the shops) right after you've fought Greed in the very last shop in the game.
  • Stealth Pun:
    • The item "Mom's Eye" makes your tears fire in two directions at once — in other words, Mom really did have an eye in the back of her head!
    • The 3 Dollar Bill's name comes from an old saying that something is "as queer as a three dollar bill", back when "queer" meant "strange" and not "homosexual". The Bill also makes Isaac happy, or to use another term, gay, back when the word meant "happy, of good cheer" and not its modern meaning. But keeping with the more modern definition of "gay", it gives Isaac a random tears effect each three seconds, which the game describes as "Rainbow Tears". The Afterbirth challenge themed around it is even called Pride Day.
    • The Ipecac item makes you shoot green bombs out of your mouth, which is literal projectile vomiting.
    • The Guardian Angel spins around you and blocks incoming shots, thus protecting you.
    • Bringing the negative down to Sheol takes you to the Dark Room after beating Satan, which was a place where photographs were processed back in the day.
    • Picking up a Cube of Meat the first two times causes it to orbit Isaac and block projectiles for him. It's a meat shield!
  • Standard Status Effects: Paralysis, slowdown, poison. Interesting case, since only Isaac gets to inflict them on enemies (with the exception of the Death boss).
  • The Stinger: "Get in the box!"
  • Stuck Items:
    • Your reusable item can only be replaced with a different one, though depending on the character, you might start out empty handed. Likewise, you can only drop a one time use item by picking up a different one, which can be stressful if you end up holding one you know would be detrimental to your health if you accidentally used it.
    • Wrath of the Lamb adds trinkets, which can only be exchanged if you find another one. Trinkets are passive abilities, so this usually isn't a problem — but there is actually one trinket that cannot be removed no matter what. This is not a bug, although it is a literal bug; the trinket in question is a Tick. Ticks are hard to remove!
      • Even worse, since the Tick can't be removed, this prevents you from picking up the Polaroid, a trinket needed to access the Very Definitely Final Dungeon.
      • Rebirth finally allows the player to drop Trinkets...except for the Tick.
      • Afterbirth finally provides a way to take off the Tick: picking up a Match Stick. Which allows you to scare off the Tick by heating it off.
  • Summon Bigger Fish: Monstro's Tooth causes the boss Monstro to fall and stomp an enemy on screen for massive damage. It doesn't work on Monstro himself.
    • The High Priestess Tarot Card summons Mom's big fat leg to stomp directly on a random enemy for major damage. Against mom, this card summons another foot to stomp you. Maybe because mom has two legs...?
    • Rebirth adds the Mom's Toenail trinket. Every minute, Mom's foot comes down to hit an enemy...and if there isn't one, it hits you instead.
  • Surreal Horror
  • Suspicious Video Game Generosity: The truly, verily, most definite Final Dungeon as of last Thursday features four golden chests, containing four powerups without any other price than the keys needed to open them. You are going to need them.
    • In general, Wrath of the Lamb buffs up the pool of available items, trinkets, powers, etc. with many powerful additions. You will most certainly need them...
  • The Swarm: Wrath of the Lamb introduced the Swarmer enemy, which appears as a husk of a humanoid head animated by a swarm of flies that are apparently using it as a nest..
  • Tactical Suicide Boss: A few.
    • In Wrath of the Lamb, Gurdy's boils are sometimes replaced by guts that spew explosives instead of regular projectiles. These will damage her.
    • Loki drops Boom Flies that, if your offensive capabilities are strong enough, you'll immediately detonate on top of Loki.
    • A canny player can push Wrath's bombs back at him, dealing significant damage. If you've got the Homing Bombs powerup, you won't even need to do that.
    • One of the new bosses in Wrath of the Lamb, Pin, can actually damage itself with its green exploding projectiles.
    • It's possible to have Mom's foot step on another part of her body, dealing a large amount of damage.
    • Satan goes down quite quickly by destroying the flying worm bombs he spawns when he's near them.
    • One of the champion versions of the Hollow is a grey version that spawns Boom Flies for every section destroyed. These can be used to blow up more sections and spawn more Boom Flies until the boss is dead.
    • The champion version of the Carrion Queen spawns little Hearts instead of the dangerous red poop. Said Hearts try to avoid Isaac and damage the Queen when destroyed.
  • Take That:
  • Take That, Audience!: The title screen, after clearing the game 200 times.
  • Take Your Time: There is no time limit of any kind, and you can backtrack as much as you want within a floor.
  • Tears of Fear: Isaac's default mode, given his crapsack childhood of abuse, harassment, and attempted filicide. When Isaac picks up a demonic upgrade, these frequently become Berserker Tears. Other upgrades or items give him Tears of Blood. And when he gets the 3 Dollar Bill, he gets Tears of Joy.
  • Teeth Flying: The Tough Love item, appearing visually as brass knuckles, allows Isaac to randomly spit teeth instead of tears. If Isaac has items which increase the visual size of his tears, he'll also shoot larger teeth.
  • Teleporting Keycard Squad: Taking an item or opening a chest in Challenge rooms triggers three waves of enemies.
  • There Is No Kill Like Overkill: There are a slew of item combinations that let you deal more damage than is actually necessary, even for bosses. Orbiting knife chains, explosive tear barrages, forming projectiles so gigantic a single tear will fill up the entire screen, the list goes on. Hell, the Game Breakers in this series is so numerous it warranted its own page.
  • Toilet Humor
  • Too Awesome to Use: Some of the Tarot cards and the Full Health pill, usable only once. Possibly some of the more powerful subweapons which can only be used once every six rooms. The epitome is the Sun Tarot Card. It is a full health pill, Necronomicon, and one-floor Compass and Treasure map, all rolled into one. It's agonizing deciding whether to use the card to see all a level has to offer, or save it for emergencies or for the final boss.
  • Turns Red: All four of the Harbingers, Gemini, Peep to a minor extent, Carrion Queen, and Mom's Heart. Some are actually less difficult after turning red.
  • Treasure Is Bigger in Fiction: Coins in this game are pretty large.
  • True Final Boss: Mom's Heart/It Lives in the original release, Satan as of the Halloween update. Isaacnote  in the original version of Wrath of the Lamb, ???note  in the updated version. In Rebirth, The Lamb, the boss of the Dark Room is this at first, until the very definitively truest final boss of the game, Mega Satan.
    • Said to be one-upped in the new Rebirth expansion, Afterbirth. Except he wasn't.
  • Underground Monkey: In both new model and palette swap flavor. Even a few bosses come in variants, some of which being Shout Outs to other games.
  • Unstable Equilibrium: Zig Zagged.
    • In general, having better items means doing better overall and and allows the player to take more risks, which in turn may improve the player's position. Doing well on the first floors greatly increases your chances of getting through the entire game. On the other hand, it's not as easy to turn things around if the first floors treat you especially badly.
    • Devil/Angel rooms are most likely to appear when you don't take red heart damage. If you're powerful and/or have many spirit hearts, you can get even more powerful.
    • Both the Self Sacrifice Rooms and the Cursed Rooms reward you with items/pickups, but require you to damage yourself. On the one hand, they're not a good idea if your HP is low. On the other hand, they're not a good idea if you have spirit hearts either, since the rewards are rarely worth them. Overall, they're still a balancing factor, since spirit hearts are bound to pop up even on below average runs.
    • Blood donation machines gives you with money in exchange for hearts. This alone rewards you for doing well, but if you use it enough, you get an item that not only gives you a heart container but also will replenishes the hearts that you spent. If you do really well on health, and have many hearts laying around the level, you get even more health.
  • Unwinnable by Mistake:
    • Thanks to a teleportation item (either pills or the Teleport! item) and some rotten luck, a player can find themselves stuck behind a room full of rocks, with no bombs to break them, making it impossible to continue, and forcing them to quit out of their current run.
    • It happened to the game author himself. In his co-commentary with Northernlion, he mentions that, after getting a certain combination of power-ups and power-downs, his firing range was too low to reach some monsters standing behind a pit — and killing all enemies is required to leave a room.
    • The Wrath Of The Lamb expansion has issues with this, with XL levels being the main culprit. The player may teleport into an area with no exits, or the game may not spawn the hatch to the next level if certain bosses are fought first in the Sequential Boss fight.
    • Wrath Of The Lamb also adds a challenge run reel, one of which is called the purist. The point is that you have to defeat the Disc Three final boss without access to item rooms. The game forces you to go up to the Disc Three Final Floor by having no trapdoor to the other Disc Three Final Floor, only a beam of light that takes you to where the challenge wants you to go. However, if you, by any means, manage to teleport yourself out of the beam of light before the new level loads, the beam will disappear from the boss room and you'll be permanently stuck on the Womb/Utero 2 with no means to get out.
      • This could, however, be deemed Unwinnable by Insanity, as players would either have to be either very clumsy or insane to teleport just as they enter the light.
    • Taking Telepills in The Chest can teleport you into an empty room that is impossible to escape from, instead of teleporting you into an I AM ERROR room like it is trying to. Unless you managed to grab another teleport before using them (either through using the pills right before you run into another Q item to take it with you or bringing "Teleport!"), you're stuck and have to forfeit the run. This is fixed in Rebirth; the I AM ERROR room in The Chest or Dark Room has a hole which resets the stage.
    • It's entirely possible to end up having a spacebar item (which appear on pedestals) appear from a chest which is in the middle of a path you need to walk through to get to the boss room... when you've already got a spacebar item, there's no other way to get to the boss room and you don't have any means of getting around the pedestal. You try to rush past the pedestal, you do the item grab pose and the pedestal pushes you back the way you came from. Now there's another item on the pedestal, but you're otherwise in exactly the same position...
  • The Very Definitely Final Dungeon: The Chest, a floor made up entirely of boss fights in almost every single room, with ??? (The Blue Baby) as the final boss. Rebirth adds the Dark Room, a dark-themed counterpart to the Chest. It's boss is The Lamb.
  • Virtual Paper Doll: Almost all of the upgrades Isaac can pick up will change the look of his sprite.
  • Turns Red: Boss!Isaac (and Blue Baby) on their last third of their health, gain angel wings and suddenly gain the ability to summon Angelic Babies and use a "beams of light" attack similar to Crack the Sky, along with firing more homing shots.
  • Versus Character Splash: Happens before boss fights.
  • Violation of Common Sense: Want God to notice your good deeds and reward you? Murder a beggar. note 
  • Whole Plot Reference: To Genesis chapter 22.
  • Womb Level: Appropriately titled The Womb, and its alternate, Utero.
  • World of Symbolism: Downplayed. A lot of the stuff is just creepy, but when you start viewing it through the eyes of an abused child... The choice of the item powerups is even worse:
    • HP ups being mostly spoiled milk and dog food, implying what Isaac is usually fed. "Nutritious" foods which give Isaac two hearts of max health include raw liver and buckets of lard.
    • Items used to beat/punish Isaac increasing his speed. (Wooden Spoon, Belt)
    • His pets all dead, presumably killed by Mom. (Tammy's Head, Max's Head, Dead Bird)
    • The Virus you often receive for beating Lust is AIDS/HIV.
    • The Brother Bobby, Sister Maggy, and Wire Coat Hanger items, implying that Isaac is a failed abortion or unwanted child.
    • The other characters being alter-egos of Isaac. He is so lonely he has to make them up in the first place (or he made them up to cope with what's happening to him).
    • The Polaroid might imply that Isaac's mom might not always have been the psychopath we know her as.
  • X Meets Y: The Legend of Zelda meets Super Meat Boy meets The Bible... in Roguelike style!

Tropes exclusive to the remake and its expansions include:

    open/close all folders 

    A-M 
  • Alternate Reality Game: The Missing Poster was intended to be used for this. What it does is obscure enough (you need to kill yourself in a Sacrifice Room while holding it), and if someone manages to figure out its effects, the Missing Poster would be used to generate a small piece of the Game Over screen. Piecing them all together would give hints on how to unlock The Lost. Unfortunately, how to unlock the reward for the ARG was discovered by data miners, which Edmund was bitter about.
    • Edmund learned his lesson and tried again. Following the release of Afterbirth, he left a clue 109 hours after the initial release. The first clue started with the icon for a new Achievement added to Afterbirth in a patch, named "Generosity". This led to a clue hunt involving a phone number, Twitter, and some digging. The end result of the ARG led to the release of a new unlockable character, the Keeper. Edmund had prevented data-mining by simply not adding the character to the game until the ARG was completed.
    • However, he did drop some hints in the game files about a new character, along with red herrings including a spritesheet showcasing the Keeper as an old man instead.
  • Ambiguous Gender: A new character, Eden, is gender-neutral to go along with their theme of randomization.
  • Ambiguously Evil: The soundtrack when fighting Satan/ Mega Satan is called Hericide, which is the killing of one's lord/master/teacher, and in the 16th ending Isaac turns into a demon.
  • Animation Bump: The game is a slightly pixellated Retraux style. The endings, however, are very fluidly animated.
  • Anti-Frustration Features:
    • When you hold up an item you're still able to move. This means you are much less likely to get hurt if you accidentally walk over a trinket/consumable during a fight, and prevents you from getting stuck if there's an active item blocking your path.
    • If the boss room entrance is facing the top, the trapdoor to the next room will be closed to prevent you from accidentally walking into it. Likewise, if your speed is almost too high to handle, you'll go over the trapdoor instead of into it to keep from going in there because you're too fast.
    • Blowing a hole through a wall to a Secret Room is now permanent; previously, one had to use another bomb to re-open the room after leaving it. Particularly helpful for cases where the room had a Slot Machine or something similar and one needs to leave to get more coins elsewhere.
    • Items now show a short tagline upon pickup that give a sense of what they do. Many just explicate what the item does, while others are more cryptic but still helpful. This can save a newcomer a trip to the wiki.
    • You can now rebind keys as you see fit, so you have a solution if you keep blowing yourself up because E is "open door/chest" in other games or you keep wasting items tapping Q or Space.
    • For the first couple of seconds upon entering a room, BBF will destroy enemies without exploding, preventing unavoidable damage in that way.
    • Curse of the Labyrinth, if it occurs on the first floor, now leaves the Treasure Rooms unlocked as opposed to requiring keys for both. Previously, this curse could easily rob a player of two items, as the low number of rooms could potentially provide no keys to unlock them.
    • The Polaroid and its evil counterpart, the Negative, are now item pickups instead of trinkets. This allows you to pick up the Tick without sacrificing a Brutal Bonus Level run.
      • Afterbirth added Missing No., which rerolls every passive item you have at the start of each floor... except for the Polaroid, the Negative, and the Key Pieces for Mega Satan, for the same reason as the above.
    • Greed mode's wave spawning can be de-activated by sacrificing half a heart to hit a button surrounded by spikes, but if you're playing as The Lost it's free, since they're a One-Hit-Point Wonder.
    • In large rooms, enemies with laser attacks will generally not fire at Isaac from off-screen to prevent the player from taking unavoidable damage.
  • Announcer Chatter: Afterbirth has a Large Ham one for calling out cards and pills. A patch made him come out at random instead of being on by default.
  • Arc Number: 109, the number of coins originally supported by the Greed donation box. The developers teased players about it and misled them into a wild goose chase for secrets, but what it meant is that a certain amount of content was simply blocked off until a patch came out after 109 hours. Coincidentally, 109 also happens to be the in-game ID of the item Money = Power.
  • The Artifact: The starting room still displays the Move, Attack, Bomb, Item diagrams, but not the keybindings, which can now be changed on the menu.
  • Ascended Glitch:
    • A certain Womb room would spawn two Larry Jrs and a Chub, but due to engine constraints the Chub would be without her third section and unable to spawn enemies. When the room was ported over to Rebirth, this "buttless Chub" was left in faithfully.
    • The Liberty Cap still retains its oddball ability to sometimes act as a compass instead of a mushroom item.
    • You can still walk diagonally through spikes and not take damage if you get it pixel perfect. In addition, one possible Curse Room layout has a Red Chest guarded by four "Eternal" fireplaces, and you can walk through those to open the chest if you're careful enough, though you can also blow them up with bombs.
    • Conquest could randomly replace War in the Depths 1 in the original game due to a glitch. Here, Conquest is both a Depths 1 and Womb 1 boss.
  • Ascended Meme: The in-game description for the Cancer trinket is now "Yay, Cancer!", recognizing a meme that spawned from the people expressing happiness at receiving Cancer (a useful trinket) and other improbable phrases that only make sense in The Binding of Isaac.
    • Additionally, beating Mega Satan as ??? unlocks a multiplayer baby called "Blue Baby".
  • Back from the Dead: Rebirth continues the trend from Wrath of the Lamb of making undead versions of existing bosses, in this case applying it for nearly all normal bosses. Note that being undead usually makes each boss even more dangerous than before.
  • Big Head Mode: Entering "T0PH EAVY" as your seed gives your character a head that's at least 5 times bigger than their body. On the other hand, entering "T1NY D0ME" gives you Small Head Mode.
  • Big "NO!": One trinket is a crossed circle whose description reads "NO! Never again!" It removes space bar items from the item pool, which is good when you're collecting stuff to randomize with the D4.
  • Black Market: In Rebirth, finding a hidden passageway beneath rocks may sometimes lead to a modified shop which lets you pay hearts for shop items instead of coins. It also has a trap door to the next level, all three beggars, and sometimes a slot machine (type varies).
  • Black Speech: The incomprehensible, guttural chanting in the Sheol theme could count.
  • Bondage Is Bad: A new item in Rebirth, "Gimpy'', is a black leather gimp mask. It's found in the Devil Room for the cost of one heart, or in regular Item Rooms.
  • Bonus Boss: Afterbirth plays with this in regards to Hush. You do have to beat it at least once with every character, but unlike Mega Satan, this boss does not end the run. Rather, it is an optional diversion that can net you some extra items at the cost of fighting an extra boss, and once you beat it, you go right to Sheol or the Cathedral.
  • Boss-Only Level: The Blue Womb contains two Item Rooms, a Shop, and a single 2x2 room with Hush in it.
  • Boss Rush:
    • Accessible by beating Mom in under 20 minutes. You have to fight through a total of 30 bosses in 15 pairs, but you're given a free item (out of four choices) to start and a second item if you win (whether they're helpful or not is another matter).
    • Mega Satan summons all the Horseman, all the Super Sins and the Angels during the battle.
  • Bowdlerise: Inverted in the credits, which thank everyone who played the heck hell out of the original.
  • Bragging Rights Reward:
    • Prior to the Afterbirth expansion, there was no practical reason to beat Mega Satan other than seeing the final ending. There were no unlocks for doing so, no achievements for doing so, not even a mark on that character's boss kill list. All you would receive was a new picture for your save file.
    • With the exception of the Lost, who has an item unlock for beating every main boss, Hard mode has no item unlocks, and its associated achievements only require you to beat Mom's Heart/It Lives to unlock co-op babies. Beating the Brutal Bonus Levels is purely for sport.
    • The unlock for beating the Bonus Boss with Keeper? Said character starts with a penny. Of course, you're earning that penny by killing what is arguably the hardest boss in the game with a borderline Joke Character.
  • Bullet Hell:
    • The battles against Mom's Heart/It Lives, Isaac, ???, and Mega Satan offer (a mild example of) this.
    • Afterbirth adds a true example of this, The Hush, an extra boss that spawns hundreds of enemies and normalizes the damage it takes, meaning even an overpowered build can't just cheese it.
  • Call Back: One of the new items in Afterbirth is actually an old item: Lusty Blood is just Bloody Lust as it worked in the original Isaac.
  • Cat Scare: The final stage of Greed Mode is named Ultra Greed. At the start of the stage, there's a boss room. You enter it, expecting a hard boss battle... and then a single Monstro (or a pack of Greeds) appears. Ultra Greed is in the next boss room.
  • Cast from Money: The Magic Fingers is an item that instantly deals a small amount of damage to every enemy in the room every time you put a penny into it. It has no cooldown time, so if you have lots of money (or are lucky enough to find the Dollar), you can spam it...until your money runs out, anyway.
  • Classic Cheat Code: Some seeds have interesting effects, such as BRWN SNKE (causes Isaac to leave a trail of poop wherever he goes) or B00BT00B, described below.
    • Taken even further in Afterbirth, where all those special seeds are now available in a list after you put one in, although the icon that indicates the list seems to indicate an Easter Egg, and can be chosen for any play, as well as removing the ability to progress in unlocks with some. They've all but been named cheatcodes. There is even one that makes Isaac invincible: ALM1 GHTY
  • Cool Hat: The Host Hat, an item introduced in "Afterbirth". It's a Host that Isaac wears on his head. It protects Isaac from explosions, and has a chance to block incoming shots and counter with the Hosts' signature three-bullet spread.
  • Color-Coded for Your Convenience: Champion enemies have traits based on their suit of color, and all of them do one heart of damage rather than half. Grey means an enemy explodes at death and drops a bomb, red means massive HP and possible regeneration with a heart drop, black drops a key, blue means it explodes into bullets on death, green leaves a trail of green creep and drops a pill, and pink generally means "less dangerous, but can still hurt you".
  • Combinatorial Explosion: Part of the update to the game is that this can now happen. The formula is no longer "pick up anything that can help you, hope for Mom's Knife or Brimstone" for a win that seems assured; now any number of items can assure victory in combination. Two wildly differing examples are Midas Touch + Book of Shadows + Nine-Volt, which basically gives you the ability to go running around turning enemies into coins every 2 rooms, and Ludovico Technique + magnetic tears + shielded tears, which give you a single controllable projectile that pulls in enemies and shots while disabling all shots that touch it meaning that you have control of basically a black hole against your enemies.
    • Another mild game-breaker is homing shots plus Technology 1 or 2. The laser beam actually curves itself around to hit enemies.
    • A further combo involves Guppy's Hairball and How To Jump. Jump over enemies to avoid them, and the hairball will plow through them. The momentum will also cause the hairball to bounce about well beyond its normal range.
    • And pretty much anything plus Brimstone. Homing Brimstone? (if combined with Spoon Bender) Triple Brimstone? (if combined with Third Eye) Ten beams firing simultaneously in all directions...Brimstone? (if combined with Tammy's Head).
  • Co-Op Multiplayer: You can sacrifice one of your hearts to allow another player to create and control a familiar. Some of these familiars have special abilities, and some are unlocked by beating Mom's Heart on Hard Mode.
  • Counter Attack: Evil (black) hearts inflict the Necronomicon effect on all enemies in the room when a full black heart is depleted. In fact, Rebirth includes many items that damage enemies when Isaac takes damage. An example is The Negative, the new counterpart of The Polaroid.
  • Cursed with Awesome: One of the random curses that you can get inflicted with is "Curse of the Labyrinth", which essentially merges two floors and forces you to fight two bosses in a row at the end. If you get it on the first floor, both treasure rooms will now be unlocked, sparing you the need for one key. On the other hand, later floors can potentially rob you of an additional Devil/Angel Room that could have spawned for both floors.
  • Damage-Sponge Boss: While there were already bosses who had this as their gimmick, this is taken to extremes as one of many gimmicks for the two new major bosses of Afterbirth, Hush and Ultra Greed, who both have health that eclipses the health of every other boss in the game and even normalize the damage you deal to them, meaning that something that would one-shot every other boss in the game will only deal chip damage to them.
  • Damn You, Muscle Memory: An odd variant—the game's new engine will trick some people up. Rebirth's new engine is extremely powerful, able to handle insane amounts of stuff on the screen at any time at a rock-solid 60fps even on lower-end video cards, but this has some unfortunate effects on people transitioning from the lower, glitchier framerate of the first. People who are accustomed to the half-second pause when transitioning into a room will routinely screw themselves over on hazards, and attacks are much harder to dodge thanks to a lack of Hitbox Dissonance.
  • Darker and Edgier: Even though the regular game is fairly grim on its own, Rebirth has a much more oppressing and bleak atmosphere, compared to the cartoony and lighthearted (if drenched in Black Comedy) atmosphere of the first.
  • Dark Is Not Evil: The Dark Bum, a demonic version of Bum Friend with a description of "He wants to take your life"... meaning he wants to take those red hearts that you can't take because your health is full and turn them into soul hearts (and the occasional spider. Being sick sucks). His usefulness (even after two nerfs) and fairly common appearance rate has pretty much made him an Ensemble Dark Horse, complete with Twitter page.
  • Death Dealer: Completely literally with the Chaos Card, which instantly kills anything it hits when thrown. It can even one-shot bosses!
  • Developers' Foresight:
    • The various insects you see—not the enemies you're supposed to kill but the actual pixel-tiny insects that add to the atmosphere—are interactive. Shoot or step on one and they'll turn into small puddles of blood. If you shoot a fly, tiny pixels of blood will fly off and they'll actually spiral downwards to the floor! If you have the Soul, bugs will be steered away from you.
    • If you're at half a heart left and you enter a new room, Isaac will pee a little at the entrance showing how terrified he (and possibly you, the player) is at what dangers this new room may present that could end your run.
    • In Afterbirth, the Flush item (which normally has no effect on bosses) instantly kills Dingle, Dangle, and Brownie when used.
    • When you defeat Ultra Greed, he turns into a giant gold statue. Midas's Touch will instantly do this, obliterating his armor reduction.
  • Difficult but Awesome:
    • Anti-Gravity Tears can be very difficult to use, but when used well you can simply drag any enemy that chases you through a path of tears, set traps for enemies that love to jump on your head, and burst down enemies that only expose themselves to damage every so often. Goes Up to Eleven with Brimstone: It can be difficult to make every laser hit, but you can now fire full-power Brimstone shots as fast as you can charge them.
    • Bob's Brain is notorious for blowing up in people's faces and generally being more trouble than it's worth. However, if you can keep track of its respawn time, keep repositioning so it doesn't immediately blow up in front of you, and Lead the Target so it hits what you want, it can function as a high-damage grenade launcher that continually replenishes itself. Particularly skilled users can even time it so that it blows up enemies when they're near bomb-able locations, saving on bombs in the long run. It shows up more frequently than a lot of items, giving players more incentive to learn how to use it properly.
  • Downer Ending: Either Isaac goes missing, or is transformed into a demon while dying. Afterbirth expands on this, showing Isaac's mother finding what's left of him inside the chest. At the underworld, Isaac seems normal enough, but a demonic shadow looms over him. Greed Mode doesn't make things any better: it shows Isaac being trapped by rocks and becoming Greed.
  • Dunce Cap: The Wiz powerup in Afterbirth is a dunce cap that gives the player character permanently crossed eyes (similarly to the "r u a wizard" pill).
  • Early Game Hell: The hardest parts of Greed Mode are often the early levels, when you have little health and only average tears and damage. Once you've gained a few items, your chances of survival increase dramatically.
  • Eldritch Abomination: In Afterbirth, collecting three Devil items transforms you into Leviathan (a mini-Cthulhu), which grants flight and a few extra black hearts.
  • Enemy Scan: The Spider Mod in Afterbirth gives every enemy (and segments if applicable) a visible health bar so you can track how much damage they've taken. It also displays how much damage your weapons are doing. Finally, the spider familiar itself wanders around randomly and can cause random effects to any enemy that touches it.
  • Escort Mission:
    • Isaac's Heart makes Isaac immune to damage, but generates a heart familiar which takes damage in his place. Enemies will target the heart instead of Isaac, so it has to be protected. On the plus side, Isaac can use any self-damage item for free.
    • The Guardian challenge gives you a character with invincibility, flight and a powerful sword to stab monsters with. The catch? You must protect a Punching Bag with Isaac's Heart attached to it. The Punching Bag takes damage, not the heart, and you have no control over how the Punching Bag behaves. You have to escort him all the way to Womb II. Most of the time, it is impossible to prevent the dude from getting hit a handful of times, though at least it tries to avoid traps in rooms. Usually. It's especially bad when you end up with charger-type bosses that can't be knocked off course, which means the Punching Bag is guaranteed to take hits.
  • Exact Words: The Suicide King card's description is "A true ending." From a Certain Point of View, it does just that, since it drops several items then kills you.
  • Fire/Water Juxtaposition: The new alternate chapters for the Basement and the Caves in Afterbirth, Burning Basement and Flooded Caves.
  • Game-Breaking Bug:
    • There seems to be a game crashing bug that crashes the game when enough damage is done to Mega Satan that they die without changing forms. It's rare, but it appears to be very consistent.
    • Sad Bombs give bombs a Tammy's Head effect. Godhead adds a giant halo to each tear. There's a glitch that allows one to let loose as many bombs as the screen will handle. Combining all three is the only way outside of Mega Satan to crash the game.
    • In Afterbirth, Ending 17 is supposed to be unlocked by defeating Hush at ???, but it only works once. On replays the player receives the exits to the next chapter instead. The problem back when the expansion was released is that imported saves from Rebirth wouldn't get the ending chest if they already had Chapter 5 unlocked. Trying to enter ??? as some characters would always crash the game, too.
    • Alluded to by the Afterbirth item GB Bug, which has the description "Game breaking bug, right away!" It adds a "glitchy" familiar that bounces around the room inflicting random status effects on enemies.
  • Gameplay and Story Integration: One of the new rooms is a bedroom where Isaac can sleep in a bed to recover health. In the center of the room, there is a rug. Blow it up with a bomb to reveal a hatch to the next floor or a crawlspace. You may want to rewatch the intro at this point.
  • Glass Cannon: Afterbirth added a literal Glass Cannon, which grants a powerful, reusable shot but also reduces Issac's health to just half a heart. A patch nerfed it hard so it takes away all three kinds of hearts.
  • Glass Weapon: In Afterbirth you can create the Glass Cannon, which is exactly what it sounds like, in every sense. It's incredibly powerful, but lowers your health to just 1/2 heart, meaning that you'll be killed in a single blow if something hits you.
  • Guide Dang It: Unlocking the Lost would be a tall order for any one player to accomplish using only the resources made available in game, so much so that the process was ultimately figured out by some people data mining and spoiling it; this unsurprisingly prompted an upset response from creators Edmund McMillen and Tyrone Rodriguez, who noted it was meant to prompt an ARG-type response with the community working and speculating to solve it. The process was meant to be a community effort, which probably would have worked eventually, but it is still fairly obscure. You either need to spend a long time going in circles and following vague clues to figure this out, though it should be noted that knowing what to do isn't half of it. note 
    • The above unlock method has been significantly shortened (but made more luck-based) in Afterbirth: Die with any character in a Sacrifice Room, while holding the Missing Poster. The difficulty is now getting both items to appear in a run, since seeded runs do not work.
    • Two stats are not shown on the stats screen, or elaborated upon at all. You have "Evil / Faith", which is a sliding scale determining what kind of special deal (Deal With The Devil or Deal With The Angel) you get when you qualify for one, and Shot Height, which is used as an alternative to range in some items that claim to increase it (notably increasing Shot Height as Azazel is a bad thing and makes his range shorter).
    • Different damage upgrades are "worth more" than others. Furthermore, some simply add to your damage stat (Damage +1 for instance), while others give you a multiplier instead, or on top of, adding to it, which is significantly better most of the time. The highest of both types are provided by, respectively, Ipecac (+40 damage) and Tough Love (3.2 damage multiplier for each tooth.)
    • Special items are back! Not only was this completely unexpected due to Edmund outright saying they would be removed, they now work differently. Instead of the huge list of Special items from the original, there are now only fifteen: Polyphemus, Mutant Spider, Brimstone, Sacred Heart, Soy Milk (no longer Special in Afterbirth), Pyromaniac, Lil Brimstone, Ludovico Technique, Dr. Fetus, Epic Fetus, the D6, Mom's Knife, Stop Watch, the D100, and Godhead. What's more, the Special counter is changed based on sight, not pickup, meaning seeing some of the bad Special items will make it less likely you'll get good ones.
    • Lazarus' entire playstyle is bizarre. He starts with a negative Luck stat (-1), and greatly benefits from dying as early on in the run as possible, since the item he starts with (The Lazarus Rags) give him a damage bonus when he revives.
  • Hitbox Dissonance: The wall-crawling spider type enemies have a damage hitbox that's extremely confusing, placed at least an inch away from the front of the actual model. Since this hasn't been fixed and the crawlers are often protected by a pit, this could be intentional to keep the game from becoming unwinnable by having extremely low range. Still, this can be frustrating when Brimstone and diagonal shots like tiny planet don't hurt them despite visibly touching them.
  • Instant Runes: The Black Powder in Afterbirth causes a trail of black powder to appear where you walk, which dissipates after a certain distance. Forming a circle with the powder forms a glowing red pentagram which damages any enemy that touches it.
  • Interesting Situation Duel: The "Challenges" give you certain combinations of items that can drastically alter the way you play. For example, the "When Life Gives You Lemons" challenge mentioned below gives you Lemon Mishap (a Joke Item) and lowers your stats, but also gives you the Nun's Habit, Nine-Volt and a single Lemon Party pill. Since your stats are so bad, you'll have to rely on leading enemies into the damaging puddle dropped by Lemon Mishap until you get better items (but due to the Habit and Nine-Volt, you can use the Lemon Mishap in almost every room, more often if you take damage).
  • Interface Screw: This game adds three new interfaces curses on top of Curse of the Lost (minimap disabled). Curse of the Unknown removes your health bar, forcing you to keep a mental tally. Curse of Darkness reduces the ambient lightning to almost nothing, though the player and most enemies glow. Curse of the Blind turns every pedestal item (activated and passive items) on the floor into a question mark, including Devil/Angel Room items and shop inventory. It'll make you think twice about picking something up.
  • Jack-of-All-Stats: Invoked by the Libra item, which actively balances your stats once you collect it. Can turn the player into a Master of None or Master of All, depending on what items it is mixed with.
  • Jump Scare: Ending 3 a.k.a. The Rubber Cement ending.
  • Kaizo Trap: Mom's Heart now explodes into a radial bullet burst when killed. It's easy enough to dodge if you know it's coming, but a surprise nonetheless.
    • Devil Rooms in Afterbirth have a chance to contain enemies that you have to kill in order to leave.
  • Last Lousy Point: Rebirth is much worse about this than the original, especially with Secret Room items. Since the Secret Room is less likely to spawn items combined with more possible variations, most players resort to exploiting the item pool mechanics to reroll Secret Room items from Beggar drops or mushroom spawns. Another annoying item is Steven, which is now impossible to find except by killing Steven in a main boss fight (already rare to begin with), and only has a 1 in 5 chance of spawning compared to Little Steven. Rerolling also doesn't work on Steven drops, so it has to drop normally.
    • Applies much less in Afterbirth: Greed Mode's restocking shops mechanic and expanded shop item pool means it is possible to see the secret room items there. As for Steven, it now drops in Golden Chests.
  • Lethal Joke Weapon: Because of the improved item synergies, many mediocre items can become the keystone to a weird yet highly effective setup. Bonus points if several if your items are bad but they become effective in tandem with each other.
    • Lemon Mishap and Pinking Shears, two mediocre-at-best items in Wrath of the Lamb, have been buffed to the point that they can singlehandedly kill bosses.
    • "A Card Against Humanity". You'd be surprised at how badly some bosses handle a room full of poop. Becomes even better if you can remotely attack through Ludovico Technique, ???'s Only Friend, or Robo-Baby 2.0.
  • Long Song, Short Scene: The Blue Womb/??? area gets a dang nice song, even though it is simply a single room before a boss fight.
  • Luck-Based Mission:
    • Eden is entirely built around this trope, starting with random stats and items. However, using them requires "tokens", which are acquired by defeating Mom. This is to prevent Save Scumming a set of good items.
    • "Dice Rooms" are rare rooms with a giant die on the floor. Stepping on it may re-roll Isaac's items, reroll the pedestal items on the current floor, reroll the pickup items on the current floor, restart the current floor, or several of the above at once. Using such a room can be the ultimate gamble.
  • The Load: Familiars have the potential to screw you over to an even greater degree than before, especially when "free-roaming" and "explosives" are dangerously mixed. Special mention goes to the BBF (essentially a friendly Boom Fly) which combines both and is liable to blow up in your face if the enemy it collides with happens to be near you.
  • Magikarp Power: One of the new ideas added to the game is the possibility of crippling yourself by picking up a bad item early, Tiny Planet and Bob's Brain to name two, in the hopes that later in the run you'll pick up an item that goes complements them really well, a high attack speed or piercing shots for tiny planet making it better than the pretty inaccurate item it is normally. One could argue it's part of what makes the game more fun than before, just the pure number of items that you might pick up and hold on to in the hopes they work exponentially well with another item you find on the run.
  • Music Is Eighth Notes: The Dingle boss whistles to summon mooks. The audio is accompanied visually by a few eighth notes.

    N-Z 
  • Nerf: An inevitable result of re-balancing the game from Wrath of the Lamb, several items and one character (Cain) were weakened for balancing purposes. On the flipside, Samson received a much-needed buff.
    • The Bloody Lust mechanic change to powering from Samson taking hits instead of getting kills is a significant change of strategy for the worse due to his starting health.
    • An Afterbirth patch nerfed Lilith's Box of Friends and Azazel's Mini Brimstone laser's power and charge time. Another patch un-nerfed Azazel's damage, but made his charge time worse.
    • Afterbirth also nerfed Judas's Book of Belial to only increase the chance of getting a Devil/Angel Room when held instead of guaranteeing one whenever possible.
  • Nice Hat: Afterbirth introduces the item Host Hat, which puts a Host on Isaac's head. The item's in-game description is even "Nice hat!"
  • Nintendo Hard: A "hard" difficulty level has been added, which significantly dials up the amount of enemies and champions while giving you less powerful items.
  • No Fair Cheating: Level seeds allow you to repeat a powerful run, but block any achievements. Similarly, challenge maps only allow you to unlock the associated achievement.
  • Not the Intended Use: The key pieces from the Angels are supposed to be used to unlock the True Final Boss. However, if the player's objective is the regular boss of that floor, then these items can be rerolled with the D6, allowing for an extra Angel Room item. Players can also bet on getting Dad's Key later to sidestep the problem, but this is less likely.
    • Also, Dead Cat (which gives you nine lives...at the cost of only having a single heart container for each life) can be used to purchase every one-heart Devil Room item for basically free: you pay for the Devil Room item with your last heart, you die, you get resurrected, you go back into the Devil Room, pick up the other Devil Room item, die again, get resurrected again, continue to the next floor with 7 lives remaining and two free items! If you're good at dodging, you probably don't need all nine lives anyway.
  • One-Hit Kill: The Chaos Card kills almost anything in one hit. The only things that can survive it are the first form of Satan, the first form of the True Final Boss, Mega Satan and, likely due to a bug, Scolex.
  • Pajama-Clad Hero: The PJs "make you feel cozy", which shows by healing Isaac to full health and giving him four extra soul hearts on top of that.
  • Power Up Letdown:
    • The general opinion of Bob's Brain. It's a minion/follower that charges into enemies in a straight line when "fired" along with Isaac's tears, exploding on contact. It will do this even if the enemy is right next to Isaac, causing him to take Splash Damage. It also doesn't explode on the return trip if it misses, making it hard to aim, and doesn't synchronize well with tears. BBF (Big Beautiful Fly) also falls into this category for exploding upon contact with enemies (regardless of location) though at least BBF's movement is predictable and can be accounted for.
    • Thought that Samson or ??? wasn't worth the effort in the original? The crappy reward-to-effort ratio for The Lost, a genuine Joke Character, is even worse.
    • The Suicide King special tarot card requires beating one of the more infuriating challenges to unlock and has the splendid effect of dropping 10 items... and killing you.
    • The Lord of the Flies transformation gives you flight, and makes all enemy flies into friendly blue flies. That's about it... At least it's free flight, but Guppy is far superior.
    • The new transformations in Afterbirth range from helpful to nearly pointless. The Mushroom, for example, is just a free Health Up.
    • Tiny Planet, which makes your shots orbit you at a fixed distance instead of going forward... which makes it almost impossible to hit anything with more than half your shots, forces you to fight at close range, and makes knockback useless for defense. At least it works differently with a few alternate attacks (notably Brimstone).
    • Curse of the Tower, unless you have an item that provides bomb immunity or invincibility after being hit. It spawns a handful of troll bombs any time you take damage, dealing lots of damage to anything in the room—but possibly also damaging you again. And it will destroy any blood donation machines or demon beggars you try to use.
    • If you manage to defeat one of the hardest bosses in the game with the Keeper, one of the hardest characters in the game, you are rewarded with... him starting with a single penny in future runs. Gee, thanks.
  • Promoted to Playable: Some of the hidden items from the original game are now unlocked from the start in Rebirth. Other items now have different unlock requirements, such as The Nail. And inverted with a few items that didn't need to be unlocked in vanilla, such as the Wire Coat Hanger.
  • Purposely Overpowered: The Stopwatch and Mega Blast. The Stopwatch significantly slows down every boss and enemy, plus their attacks, for the rest of the game, but requires you to put 999 coins in the Donation Machine (which will take dozens, if not hundreds, of runs, even if you somehow get The Dollar nine times in a row, as the Donation Machine will jam up after putting in a random number of coins). The Mega Blast is Brimstone or Krampus' Head on crack, since it's pretty much one giant Brimstone laser that lasts a solid 15 seconds, and lasts between rooms (so you can pretty much steamroll every single room you enter during that time). However, this requires beating Mega Satan with every character, including the Joke Character AND it's the only item in the game with a 12-room charge (and batteries only refill 25% of the charge bar), so you'll only be able to use it once every two floors, or once a floor if you're lucky.
  • Recurring Boss:
    • Depending on your choices and luck, you may fight The Fallen as a boss four times in a single run: once at a random level, once during the boss rush, once as a Double boss in the Womb, and once guarding Satan. Not counting the times it shows up as a regular room enemy and its slight recoloring Krampus.
    • Similarly, the Greed/Super Greed battle is almost guaranteed to replace one of the shop rooms or secret rooms you've striven to unlock. Bonus points if the two show up on consecutive floors.
    • There are four completely different Gurdy bosses for various stages in her life cycle, which can be fought in each of the four main areas of the game. You can potentially fight them all in one run.
    • In Greed mode, you are naturally quite likely to fight several copies of Greed and/or Super Greed on the penultimate level, then fight several more copies at the beginning of the final level. And then you fight Ultra Greed.
  • Retraux: Rebirth's art style is intended to resemble a colorized Gameboy game. Additionally, there is an arcade filter available by using the B00BT00B seed code. Afterbirth adds a Retro Vision pill which pixelates the screen on and off for a minute or so.
  • Rock Me, Asmodeus!: Hericide, Satan's new boss theme.
  • Save Scumming: Intentionally discouraged with the increased item synergies in the hopes that players stop immediately restarting when they get a bad item early on. Then again, the seeding tools provide for a form of this if one gets particularly lucky with their game's generation and want to retry after dying partway through.
    • Also discouraged with Eden. Eden starts with random stats and items, so selecting Eden requires and consumes an Eden Token gained by beating end-game bosses. But if you're a good enough Isaac player you'll have more Eden Tokens than you know what to do with.
    • By forcing the game to quit before the Game Over screen comes up you can reload your last suspend save, but never collect Guppy's Collar while doing this. The game forces 1-up effects when you save scum and the Collar works by either reviving or killing you.
  • Schmuck Bait: There's an unlockable tarot card called Suicide King. Upside, it spawns a bunch of cool pickups. Downside? You die.
  • Secret Character: A new one for this version. "The Lost", a One-Hit-Point Wonder incapable of gaining any hearts and starts with flight. You get him by dying to Mullibooms as Isaac on the basement, to your own bombs as Maggie in the caves, to Mom as Judas, and to Satan stage 2 as Azazel, with no deaths in-between and in that order.
  • Sequel Difficulty Spike:
    • Zig-Zagged. Rebirth adds a lot of new content while updating older items from the original, which makes things both more difficult and easier thanks to the new items but larger item pool. The shop gets a major revamp with a lot of very useful items to potentially buy. The main bosses are a straight example, all of them having been given new moves and Bullet Hell abilities which make the fights twice as hard as they were in the original game.
    • The Afterbirth expansion adds new features to the level design such as cramped rooms and trap rooms. Multiple bosses at cramped rooms don't mix well. And certain trap rooms only give you a split second to react before a bomb explodes in your face. There are also trapped treasure rooms which might require you to use a bomb to reach the item.
  • Silliness Switch: Some special seeds you can type in have strange and sometimes hilarious effects. For example, FART SNDS turns all sound effects in the game into, you guessed it, fart sounds. Find a nickel? Pffrt. Open a door? Ffrrp. Take damage? Prpfff. Another good one is SLOW 4ME2, which increases or decreases the background music tempo depending on how fast you're moving.
    • As of Afterbirth, inputting a special seed permanently unlocks its effect, and any number can be toggled in a new menu of Easter Eggs.Spoiler 
  • Solid Gold Poop: In Rebirth, any run-of-the-mill poop piles you find have a chance to be golden poop piles, which drop a bunch of coins or the Counterfit Coin trinket when destroyed. Having The Poop active item and Midas' Touch will let you spawn these every single room.
  • Speed Run:
    • Now actively encouraged, since many features were added to help out the dedicated Speed Run community. All runs have an internal timer attached to them (viewable by pulling up the map, which also displays the current level for screenshot purposes) and the game keeps track of your best times for fresh runs as each character (i.e. randomly generated, not from a seed). The main purpose of seeds was to allow for many people to play the same run and compare completion times, since without seeds the times were too often influenced by the Random Number God. There are now leaderboards for the quickest runs for a particular daily seed and competitive speed-running may very well arise.
    • Additionally, beating Mom in under 20 minutes grants access to the special Boss Rush room. The little clock that's visible during each loading screen shows how much time is left until this room expires, and you can bring up the map to check your current time.
    • The Speed! challenge requires you to beat It Lives in 16 minutes, or every 10 seconds you take a half-heart of damage. On top of that, all enemies and their bullets move twice as fast.
    • In Afterbirth, defeating Mom's Heart/It Lives in under 30 minutes grants access to The Blue Womb and the Bonus Boss Hush.
  • Spread Shot: Where to start? Several enemies use these, and there are many items that allow the player to fire in spreads.
  • Standard Status Effects: The Iron Bar item adds a Concussion tear effect, which confuses enemies. The Charm tear effect causes enemies to actively seek out and damage other enemies, if they are capable of doing so (enemies stuck on a certain path, such as rolling guts, don't seek out other enemies); the charmed enemy can still damage you, however. The Fear tear effect causes enemies to slowly run away from you, and stops some enemies from firing at you. The Fire tear effect deals some brief continuous damage after hitting an enemy, and causes occasional fiery explosions. The Slow and Poison effects return from the original game. They're unchanged except affected enemies now have an icon above their heads.
  • Stealth Pun: The Latchkey gives you Luck and Keys.
  • Stonewall: One of the new items, Punching Bag, gives you a friendly Mulligan that acts as a tank for you.
  • Stuck Items: You're still stuck with whatever is held in your use slot like in the first game until you find another usable item. However, it's thankfully averted with pills, trinkets and tarot cards, which can be dropped by holding down the map button (or the left Ctrl button on your keyboard). But even the map button cannot get rid of the Tick trinket, which is the one truly irremovable item in the game.
  • Super Prototype: Technology 0.5 is a far superior laser when compared to Technology and Technology 2. It doesn't replace your regular tears so is a direct firepower upgrade when you pick it up, doesn't have a damage multiplier reduction built into its stats and perfectly synergizes with your power-ups. It also randomly adds power-up effects. Its only downside is that it occasionally misfires, but you'll barely even notice it.
  • Suspicious Video Game Generosity: The item pool got buffed *again* from Wrath of the Lamb by introducing items that confer benefits worth two separate items from "Vanilla" Isaac. You'll need those buffs for sure...
  • Talking Poo: The Dingle boss, and his minions (Squirts).
    • Afterbirth adds Dangle and Brownie.
  • Theme Naming: The Disc One Final Bosses and the True Final Boss all have boss themes that end in cide. (Matricide, Ventricide, Hericide, and Infanticide. Averted with the fake True Final Bosses, who have uniquely named themes (Ascension and The Fallen Angel)
  • Thief Bag: In Afterbirth, money bags will occasionally spawn that drop a few bombs, coins, or keys when grabbed.
  • Too Awesome to Use:
    • The Friendly Ball allows you to "capture" an enemy and release it to fight with you until it dies, persisting between rooms and floors. However, since the item has a 4-room recharge, it can take at least eight rooms in order to successfully release an enemy you captured, and even then your new companion will most likely die after a couple rooms.
    • Mega Blast is an activated item which fires a massive Brimstone laser which does insane damage and persists between rooms and floors, lasting for fifteen seconds. However, not only does it have a 12-room recharge (the only item in the game to require that many rooms), but the battery pickup will not fully recharge the item for another go. Because of this, Mega Blast tends to be saved for endgame floors/bosses that players want to wipe out quickly, such as the insanely tanky Bonus Boss.
    • The Chaos Card can One-Hit Kill literally anything in the game. The catch, of course, is that it's a card and can therefore only be used once. Like Mega Blast above, the Chaos Card tends to be saved for endgame bosses such as said insanely tanky Bonus Boss. Unless, of course, the player gets a Blank Card...
    • Diplopia is an activated item that doubles every pickup and collectible item in the room. With the number of items in the game that stack with themselves, this can create some insane synergies. However, it's only good once, and you can't cheat by using the ? Card to duplicate its effect because doing so consumes Diplopia anyway for no additional benefit. It often comes down to a decision regarding whether to use it on the decent item you have in front of you, or to hold onto it in hopes of getting a better item to duplicate later on.
  • Took a Level in Badass: A number of characters, playable and otherwise:
    • Mom's Heart/It Lives was a rather straightforward Flunky Boss in the original game. This time around... let's just say that Bullet Hell veterans will feel right at home.
    • Isaac/??? likewise get a bullet hell buff and new attacks.
      • Isaac's third form is considerably easier in Rebirth - his light attacks are easy enough to avoid as you can guess the pattern of the safe zones, plus his bullet hell attack has a much shorter range, is easier to dodge and is not homing. And he doesn't spawn angels in this phase.
    • Eve has more health and Whore of Babylon kicks in at one full heart instead of a half, allowing her to take advantage of the serious damage buff while still being able to endure a blow from most early game enemies, giving her a chance to build up a buffer of spirit hearts.
    • Samson has much more health, increases damage done for every hit he takes, has much larger range, and keeps accrued bonuses across the entire floor instead of just the room.
    • Most characters receive an upgrade to their starting load out once certain conditions are met. Such as Cain starting with the Paper Clip (unlocks Gold Chest for free) or Eve starting with the Razor Blade (boost damage for the room at the cost of a heart, letter her trigger Whore of Babylon at will).
  • True Final Boss: Attempts always end after a certain boss, though unlocking more stuff and meeting certain requirements can result in the bar being raised on who is considered the final boss; for example, the very first run ends with Mom at stage six, though beating her a second time spawns the door to the next stage, where players have to fight the new final boss, Mom's Heart. Assuming everything is done perfectly, you have to reach the credits eighteen times to unlock The Very Definitely Final Dungeon and face the 8th final boss.exp.(spoilers!) 
    • However, with a bit of Sequence Breaking using a Devil Room that spawns after the Mom's Heart fight, which always leads to Sheol even if you haven't yet unlocked It Lives!, one can theoretically reduce this to eight runsexp.(spoilers!) . Still quite a few runs though.
  • Unexpected Gameplay Change: Some challenges take away your tears completely and force you to fight with either attack familiars or a recharging spacebar item and maxed bombs.
  • Unique Enemy: There's a blue-skinned variation of the Conjoined Fatty monster that has a very slight chance of appearing in the I AM ERROR room and the Chest. Despite what its appearance may imply, it's completely distinct from a champion variant and attacks with vicious homing Ipecac shots.
    • The bosses Hush and Ultra Greed spawn Gapers that are reskinned to fit the respective boss's motif. Hush also spawns uniquely-skinned Ring Flies that form more complex formations than the normal variety and reskinned Boils with a different attack pattern.
  • Unwinnable by Mistake: The Blue Bomber challenge turns off your tears but gives you the Kamikaze spacebar item and Pyromaniac (immunity to bombs). Some enemies, however, are immune to Kamikaze, so you need bombs or another source of damage to kill them. If you have neither, you have to reset. Mercifully, a patch added Brother Bobby to the player's arsenal, which prevents the situation from being completely unwinnable.
  • Up to Eleven: Afterbirth has the XXXXXXXXL challenge, which is the "XL" level effect on steroids. All levels have a size which is roughly equal to an XL Womb level.
  • Variable Mix: If the room has a lot of enemies or there's a miniboss, an electric guitar harmony fades into the music.
  • Violation of Common Sense: With a hard cap of 12 hearts compared to the original having no cap at all, it's actually to your benefit to only have a few red hearts. Having full health means you will be unable to pick up spirit hearts or the new black hearts (which deal full room damage when depleted, similar to the Death tarot card). This means runs in which a low number of health containers are found may actually be more viable. It also seems that spirit hearts are a bit more common, and black hearts are more likely to pop up than you might expect for something so useful.
  • Western Zodiac: The 12 signs of the zodiac appear as upgrades for Isaac.
    • Aries increases speed and lets you deal damage to enemies by running at them.
    • Taurus slows the player down, but when in a room full of enemies you build up speed over time, eventually getting the My Little Unicorn effect.
    • Gemini gives Isaac a little buddy attached to him that attacks enemies when they get close.
    • Cancer gives 3 soul hearts and makes all damage reduced to 1/2 a heart when he takes damage in a room.
    • Leo allows the player to break rocks, mushrooms, skulls, etc. by stepping on them.
    • Virgo has a chance to make the player invincible after taking damage and makes all negative pills positive.
    • Libra balances the player's stats and gives 6 coins, bombs, and keys.
    • Scorpio gives the player's tears poison effects.
    • Sagittarius makes the player's tears penetrate enemies and increases speed.
    • Capricorn increases all stats.
    • Aquarius leaves a trail of tears behind the player, damaging enemies that step in it.
    • Pisces increases tear fire rate and the amount of knockback enemies take from tears.
    • Finally, the Zodiac item takes the effect of a random zodiac sign every floor.
  • Wham Episode:
    • The 15th and 16th ending. Respectively, Isaac is shown to have gone missing, with his mom searching for him, and Isaac turns into a demon!
    • Ending 17 and 18. The first confirms Isaac died trapped inside the chest. The latter is another take on his death: he's crushed by debris while trapped on some cave and his corpse becomes Greed.
  • Winged Soul Flies Off at Death: The new death animation. And it's a top secret character, called "The Lost"!
  • A Winner Is You: Inserting coins into the Greed Donation Machine grants you a few unlocks for the first hundred or so. Originally, it stopped at around 109, but a patch allowed the player to set the donations towards 999, which does nothing but praise the player with fireworks at the end and award an achievement. But something major happens if you donate one more coin...
  • When Life Gives You Lemons: The name of Challenge #12.
  • World of Symbolism: Isaac explores the same themes as most of Edmund McMillen's older games, such as Time Fcuk, but uses very different imagery to do so.
  • Wrap Around: The Continuum item grants this effect to your tears, causing them to pass through walls and emerge from the opposite side.


Today I died. I was killed by this page on some wiki. (ugly)
I leave all that I own to my pet cat Guppy. (Pretty cool stuff!)
Goodbye cruel world,
-XOXO Troper

Alternative Title(s): The Binding Of Isaac Rebirth

http://tvtropes.org/pmwiki/pmwiki.php/VideoGame/TheBindingofIsaac