A character in The Binding of Issac that used to be the final boss before Repentance came out. The boss was and is still controversial due to even being able to have the opportunity to fight the boss is up to chance unless the player has beat Hush during that run, in which case there's no chance and it's just a guarantee. Delirium is depicted as a white floating head with yellow eyes, and can mimic the appearance of other bosses and their movesets.