The Boss Room is a room where the current floor's boss is fought, and the boss must be defeated in order to progress to the next floor (unless Isaac is teleported to the I AM ERROR room or uses the We Need To Go Deeper! item).
The room has a frame made out of bones and the room symbol and top of the door frame is a skull.
In the Boss Rooms on non-final boss floors, the song "Divine Combat" (regular Bosses) or "Crusade" (Wrath of the Lamb Bosses) plays in the background during the boss fight. In The Depths/Necropolis II, which plays "Thine Wrath..."; The Womb/Utero II, which plays "...Be Done"; Sheol, whch plays "Enmity of the Dark Lord"; and The Cathedral and The Chest, both of which play "My Innermost Apocalypse". Once the boss has been defeated, the song "Peace Be With You" plays.
Up to two Hearts and/or Soul Hearts are dropped after defeating a boss, one less if the Everything is Terrible secret is unlocked. Bosses that are Champions are also more likely to appear after said secret is unlocked.
- If the Curse of the Labyrinth curse is activated for the current floor, it will contain two Boss Rooms. If it is activated on The Depths/Necropolis or The Womb/Utero, you will fight the two bosses in the order you would fight them if the floors were separate, and Thine Wrath... and ...Be Done will be played for both bosses on their respective floors.
- The IV The Emperor tarot card teleports the player inside of the Boss Room.
- It is possible to teleport out of a Boss Room, just as any other room. If the boss is not yet defeated and you teleport out, the player will be forced to re-fight the boss, with its health completely restored. It can also turn into a Champion variant.
- If you have Dead Cat or 1UP, killing a boss and then killing yourself with a Bomb will respawn Isaac in the previous room. You can then fight the boss again for another item, with the trapdoor still open. This can be exploited to gain a large number of items. This no longer works in Eternal Edition.
- Alternatively, spawning a Fly by using a Portable Slot or Slot Machine (created with a Wheel of Fortune Tarot Card) after defeating the boss, and then exiting and re-entering the room will allow you to fight the boss again. This can also be done by spawning a Spider by killing a Devil Beggar with a Bomb (the Devil Beggar has a chance to appear when Judgement Tarot card is used).
- A rare bug can cause no boss to appear. As no boss can be defeated, the trapdoor will also not appear and the level cannot be completed.
|Rooms in the Wrath of the Lamb|