Delirious

Effect

Upon use, spawns Delirium in a form of a friendly boss for the current room.
Changes the appearance of the current room so it looks like a different chapter.

If multiple bosses are spawned in one room with Car Battery, The Battery, or batteries, the bosses can try to kill each other.
Sometimes bosses don't spawn because of grid entities getting in the way. When this happens the upper door appears to have friendly particles.
(Removed in Repentance) Unlike Mega Blast, this item can be charged with a single Lil' Battery.
It is possible for Hush to spawn, despite Delirium not transforming into Hush during its boss battle.
If a boss summons monsters, the monsters will be charmed and will follow Isaac out of the room.
Delirious has a 60% decreased item pool weight, making it less likely to appear than other collectibles.

(Added in Repentance) Book of Virtues: Generates a white wisp that resembles one random boss from this list:
- (Monstro) Monstro: Fires an inaccurate spray of 6-10 tears at a time, similarly to Monstro's Lung but without the charge time.
- (The Duke of Flies) The Duke of Flies: Each wisp will create and can have up to 3 Blue Flies out at a time, similar to Rotten Baby.
- (Loki) Loki: The direction the tears are fired alternates between the cardinal and ordinal directions, similar to Loki's Horns.
- (The Haunt) The Haunt: Fires Brimstone lasers. The laser does not need to be charged to be fired, and can tick up to 8 times for a total of 8 damage.