せん妄
One of many true final bosses of [i][[The Binding of Isaac]][/i], introduced in [i]Afterbirth+[/i]. It initially looks like a giant melting [[skull]] with small [[yellow eyes]].

Aside from some basic [[danmaku]], its main ability is to shapeshift into any boss previously encountered in a given run.

[spoiler]Due to the nature of the boss and its lair, Delirium is widely speculated to repesent Isaac's mind falling apart as he suffocates inside of a toy chest he locked himself into.[/spoiler]
delirium