(Not to be confused with the Boss Challenge Room)
(Not to be confused with the Eternal Challenge Room)
The challenge room can be recognized by the Gauntlet Door (a pair of crossed swords above the doorway).
It can only be entered if the player is at full health (or the equivalent of full health, made up with Soul Hearts). It is also possible to enter the challenge room without full health if it borders a secret room and you blow up the wall in the secret room that leads to the challenge room; however, you can't use bombs to exit the Challenge Room until you have finished it. Having the XRay Vision item makes it possible to leave back into the Secret Room, though.
Note that full health is necessary regardless of the number of hearts available at the start of the level. If you have Soul Hearts, they must also be full. Using items that increase health in order to reach the level of red hearts that would have represented full health at the start of the level will be insufficient. For example, if the player starts the level with 5 red hearts, and subsequently upgrades to a life maximum of 6 hearts, then 6 hearts will be necessary to enter the challenge room.
Once inside, the player will find a Chest or an Item. Upon opening the chest or picking up the item, the player will have to defeat three waves of enemies (or bosses on later levels) before being able to exit the room, and like normal room filled with enemies, a Pick Up may spawn in the center after defeating all enemies. This room can appear from The Basement 2 onwards.
The waves of enemies spawned depends on the floor, and it's randomly chosen between two available ones.
- The remaining waves may spawn all at once by doing one of the following things:
- Pressing pause immediately after taking the loot from the room
- Unlocking something just as the waves are going to spawn
- Using an activated item
- It is possible to teleport out of a challenge room, just as any other room. After teleporting out, the enemies will disappear (i.e. will not be present upon reentry). However, if the enemies are not destroyed and instead evaded in this way, they will respawn upon pickup of a collectible item.
- For example, the challenge room may feature the Teleport! item in the centre of the room. It is possible to pick up this item and immediately use it to avoid fighting the enemies. However, reentering the room and swapping out your Teleport! item back for the original item you left behind (if you swapped them upon pickup) will cause enemies to spawn.
- If you use Dad´s Key to escape a challenge room, the game´s music for the challenge room will keep on playing until the music ends.
- Challenge rooms are only spawned if the player has full health when the level is generated (soul hearts will add up as well).
- Challenge Rooms allow for the possibility to pick up two identical items on the same floor.
- The first wave will also spawn if you pick up any item inside the room (such as an item from the Beggar), not necessarily the item in the middle.
- Having flight allows you to enter challenge room without full health.