It is unlocked by defeating Hush. Each room in this chapter takes the form of a different chapter, ranging from The Basement to The Chest and Dark Room , including variant chapters like The Cellar and the Burning Basement. The Void is extremely large compared to other floors, and it is the only floor in the game not counting XL floors to contain multiple boss rooms. Most of them contain random bosses from other floors, including some of the final bosses, such as It Lives , Satan , Isaac , etc. One of them, however, contains the main boss of the floor, which is always Delirium.
It is assumed to be one of the true final bosses appearing in final chapters of the game, along with Mega Satan. Delirium's true self is a gigantic, white skull-resembled entity sporting large eye-sockets consisted with black eyes and yellow iris. Its mouth sport long vein-like "stitches", similar to Hush. From all forms Delirium takes, each are identical to respective bosses from the previous chapters, except with Delirium's own colors, including white colors, yellow eyes, and a "melting" mouth.
It is the final boss of The Void and is the final boss of the series as a whole. Can apply up to 5 to a single Map item. Defeat Delirium! Cross stitch your favorite boss from rogue-like indie game the Binding of Isaac Boss: Delirium Design area: 7. Ten years in their hands, he's happy to be someplace safe.