Devil Room

The Devil Room is a special Room that has a chance to appear after defeating a boss, although it is rare. There are multiple factors that increase the chances of a Devil Room spawning, such as possessing a Pentagram, killing a Beggar, etc. The Devil Room may also be accessed via the Joker Suit Card, or randomly with Red Chests, which will cause Isaac to return to the starting room of the floor upon exit.

When in the room, two items from the Devil Room's Item Pool are shown, which can be bought with, depending on the item, 1 or 2 or even 3 Heart Containers or occasionally Soul Hearts.

There is also a 10% chance that a special boss called Krampus will appear in the room upon entry once per playthrough. In this case, there will be no items available to purchase, and he will drop A Lump Of Coal after the battle. This item can be re-rolled with The Dice into another item from the Devil Room Item Pool.

Under certain conditions, an Angel Room replaces the Devil Room.

Notes[]

The simplest way to unlock the Devil Room is to simply take no red heart damage throughout the entire level (this includes damage from enemies, projectiles, spikes, etc). You can still take damage if you have Soul Hearts, but all Soul Heart damage taken lowers the chance of the room appearing slightly.
When playing as ??? or any characters without any heart containers upon entering the room, all items will cost 3 Soul Hearts.
If the player has no Soul Hearts and buys an item for exactly as many or more red heart containers than they currently have, Isaac will die.
If the player has no red hearts and tries to buy an item for red hearts, Isaac will die.
If the player has Soul Hearts and buys an item for more red heart containers than they currently have, Isaac will lose all heart containers and Soul Hearts, and will die from a single hit until more Soul Hearts or heart containers are collected.
If the player has no red hearts and has less than three Soul Hearts Isaac will die when buying an item.
If the player has Soul Hearts and buys an item for exactly as many red heart containers as they currently have, Isaac will keep his Soul Hearts.
Without any heart containers, the gameplay functions exactly like ???, making red hearts and red heart-related items useless until more heart containers are obtained, along with other special effects such as Whore Of Babylon always being active.
Isaac dies if he has a single heart container and an Eternal heart then makes a deal costing more two or more hearts.
Judas' Tongue sets the price of all Devil Room items to 1 heart container, but all soul heart deals will remain the same.
The Devil Room on The Womb 2 will always contain a trapdoor to Sheol instead of two items. This makes it possible to enter the level before unlocking It Lives!.
Invincibility granting items such as Book Of Shadows will not make the items free of health costs, unless you are playing as ???, where items that grant invincibility will allow you to "steal" Devil Room items. However, they will prevent Isaac from dying if he has no Soul Hearts.
Doing a deal with the devil counts as damage for the purpose of "No Damage" achievements.
If The Dice is used in the room, the items being sold can be re-rolled into other items from the pool, but the cost of Heart Containers will not change. This makes it possible to get items that cost 2 heart containers for 1 heart container only.
The Devil Room will not appear after beating the very first level in any case (The Basement 1 or Cellar 1). However, it can still be accessed with The Joker Tarot Card.
If the very first level is an XL map (Basement XL or Cellar XL), the Devil Room may appear after beating the second boss.
Temporary health boosts such as those from the XI Strength Tarot Card or Liberty Cap will not reduce the number of heart containers lost from a deal. Going out of the room will remove the extra heart container, if any
If player has a judgement card and uses it inside devil room the beggar will pay out in items you would get in a devil room. (Has to be inside devil room otherwise will have normal chance.)
If you end up with exactly zero hearts after a deal with the devil (and no soul hearts), Isaac will die. If your deal would end up with negative red hearts Isaac will live, even without any soul hearts (Warning: If you do have soul hearts while taking this deal, you may lose most of them). Taking a deal while having no hearts at all will kill him.

Probabilities[]

The basics: The Devil Room can spawn once you clear the level's Boss Room or reenter Boss Room After clear based on your accumulated probability. It cannot spawn in Sheol, although they can be accessed on those floors via the Joker card, or a red chest teleport. If you get a Devil Room in The Womb 2 after beating Mom's Heart (before you beat Mom's Heart for the tenth time), you won't get any deals, but a trap door leading to Sheol. If you have beaten Mom's Heart at least ten times, there will spawn a regular trap door in the Boss Room after beating Mom's Heart and you don't have to find the Devil Room in order to get to Sheol.

Base probability = 1%

Add the following percentages:

Have only one Pentagram: +20%

Have multiple Pentagrams: +30%

Have Book of Revelations: +35%

Have Book of Belial: +25%

Killed 1 or more Beggars in current level: +35%

Took no red heart damage from the boss: +35%

Took no red heart damage in current level or Devil/Angel Room appeared the last time Isaac visited the boss room: +99%

Then multiply by one of these:

Devil/Angel Room last spawned in a level 1 less than your current level (or greater; see below): 0.25

Devil/Angel Room last spawned in a level 2 less than your current level: 0.5

The level number the last Devil/Angel Room spawned on is not reset when you start a new run. This means, for example, if you get the Devil Room on Womb 2 in a run and then start a new run, you will continue to be affected by the 0.25 multiplier throughout the whole run until you spawn a new Devil/Angel Room in a sufficiently early level and get 2 or more levels below it (of course at 2 below you will be affected by the 0.5 multiplier instead). Due to this behavior (which is probably a bug), it is recommended to restart the application after every run to maximize your chances of spawning this room.

The shell game beggar in Arcade is also counted. Self-inflicted damage is not counted. (e.g. Razor Blade, Blood Rights, IV Bag, Bad Trip, Blood Donation Machine, Devil Beggar)

The strange/unimportant rules:

The room didn't appear once you killed the boss: probability = 0%

You cannot see a devil room if you defeat Mom in the Depths 2. But if you teleport out of the room (even using the Emperor tarot card), you may gain access to the devil room (if it had spawned), since the boss room layout changes to the normal one (no sealed exit).

Devil Room Items[]

For the "cost" section of the following table, HP = Heart container. All items may also appear at the cost of 3 Soul Hearts per regular heart container instead of their normal cost.

Item	Icon	Effect	Price
The Book Of Belial		Adds 2 points of damage for the current room. Damage is further multiplied by 1.5x with the Blood Of The Martyr item. Also increases chances of a Devil Room spawning by 25%.	1 HP
The Book Of Sin		Spawns a random Pick Up, Pill or Card.	1 HP
Brimstone		Changes tears to a chargeable laser, which pierces all objects in its path. Also multiplies damage by 3. It can only be fired after a short charge-up period.	2 HP
Brother Bobby		Follows Isaac around shooting normal tears.	1-2 HP
The Common Cold		Gives Isaac's shot a chance of poisoning enemies for a 2.5 seconds, and turns tears green.	1 HP
Dead Cat		Your HP is set to 1. You are followed by a floating cat head and have 9 lives (these still count as deaths on the statistics screen). You can increase your max HP as normal, but after each death it will reset to 1 again.	2 HP
Demon Baby		Follows Isaac and automatically fires at enemies in its reach.	2 HP
Forget Me Now		When activated, the level ends and is freshly regenerated with new rooms, monsters, and items. Disappears after use.	1 HP
Lord Of The Pit		Isaac can fly over all obstacles, including damage floors, spikes, rocks, and pits. Increases speed by 1.	2 HP
Lucky Foot		All Pills picked up will have positive or neutral effects (same effect as the PHD, but without pill identification and neutral pills). Increases the chance of getting Pick Ups from clearing a room or from Poop and Fireplaces. Increases the chance of winning the Shell game in the Arcade room from 33% to roughly 50%. Increases the chances of getting items from Golden Chests.	1 HP
The Mark		Increases Damage by 1, Speed by 0.2, and adds one Soul Heart.	2 HP
Mom's Knife		Once collected, Isaac no longer shoots tears, he shoots a knife in boomerang style. The range of throw increases by charging the shot. Can also be used as a melee weapon while not fired.	1 HP
Money = Power		Increases damage based on the number of coins the player has at the moment.	1 HP
Monster Manuel		Summons a random familiar for the current room only, even if it is locked.	1 HP
The Nail		On activation, adds one Soul Heart and allows the breaking of Rocks and damaging enemies by simply walking over them. Increases Damage by 0.7 and decreases Speed by 0.18 for current room.	2 HP
The Necronomicon		Damages all enemies in the room significantly.	1-2 HP
Ouija Board		Turns Isaac's tears spectral, allowing them to go through rocks or obstacles.	1 HP
The Pact		Increases Damage by 0.5 and Rate Of Fire by 0.7. The player also gains 2 Soul Hearts.	2 HP
The Parasite		Makes the Isaac's tears split in two when they hit something.	1-2 HP
A Quarter		Gives you 25 pennies.	1 HP
Razor Blade		Deals 1 Heart of damage to Isaac, which increases damage for the current room.	1 HP
Sister Maggy		Follows Isaac around shooting blood tears.	1 HP
Technology		Gives Isaac a laser shot with unlimited range. Shots pierce enemies but not rocks, fire, or poop. Shots can't be angled, and will not provide knockback.	1 HP
We Need To Go Deeper!		Creates a trapdoor to go to the next floor. If used in The Womb, it will create a trapdoor to Sheol, even if the player hasn't unlocked it. Does not work in Sheol, The Cathedral, or The Chest.	1 HP
Whore Of Babylon		When Isaac reaches a half-heart, he is given +2.16 damage, and his speed increases by 0.3.	2 HP

Wrath of the Lamb DLC[]

Item	Icon	Effect	Price
Guppy's Head		Spawns 2-4 Blue Flies to damage enemies.	1-2 HP
Guppy's Paw		Removes one Heart Container in exchange for gaining 3 Soul Hearts.	1-2 HP
Bloody Lust		Increases damage each time Isaac kills an enemy for the current room. (.28 damage per kill, caps at 3.3.)	2 HP
Guppy's Tail		Increases chance of gold chests and normal chests.	1-2 HP
Spirit Of The Night		Grants Isaac flight and spectral tears.	1-2 HP

Bugs[]

If you are playing as ??? with The Wafer, buying any item for Soul Hearts will only cost half a Soul Heart, instead of 3 Soul Hearts.
Any invincibility-granting item can allow you to buy items that cost Soul Hearts for free, as long as you have at least 3 Soul Hearts.
If you use momentum and grab both items while moving, it will take the heart container payment for both while only giving you the first Item.
Buying the Dead Cat item with 2 or less heart containers will cause Isaac to die and then respawn with 8 lives in the previous room.