The Void

The Void is a new chapter added in the Afterbirth+ expansion. 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 Burning Basement. The Void is extremely large compared to other floors, and it is the only floor in the game to contain multiple boss rooms. One of them contains a random final boss, another contains Delirium, and the others contain random bosses from other floors.

Access

The Void is unlocked by defeating Hush. After defeating Hush at least once, a new exit will appear in the upper right hand corner of the 2x2 boss room in which Hush was fought. The new room contains nothing except for a Portal. It does not spawn enemies and serves as the entrance to The Void (the animation shows it trying to suck Isaac in but it's only visual).

After unlocking The Void, the portal can then appear after every major boss starting with Mom, even if Hush was not defeated in that run.

The deeper the boss, the higher the spawning chance:

• 5% after Mom (Only if Isaac has 100+ tear damage or 20+ items)
• 10% after Mom's Heart/It Lives
• 15% after Isaac or Satan
• 20% after ??? or The Lamb
• 50% after Mega Satan (If the portal appears, the run will not end instantly like it normally does)

Defeating Hush will still guarantee entrance to The Void.

Notes

• The portal can appear multiple times during a single run.
• Although the Portal leading to The Void may not appear after defeating Hush for the first time, leaving and re-entering Hush's room will make it appear.
• Since The Void has multiple boss rooms, using the The Emperor card will teleport Isaac to one of them randomly. This could also crash the game as well, so it's not recommended.
• After beating Mega Satan, the Void portal appears behind the chest that would normally end the run.
• If the portal spawns below your position after defeating a boss, you will immediately enter The Void.
• Jumping into a trapdoor will reset The Void, an effect identical to Forget Me Now. This is useful if you've explored everything but need to clear more rooms to acquire health items before the final fight. The trapdoors must be found under rocks, as We Need to Go Deeper! and the Ehwaz Rune does not work.
• Similarly, going to an I AM ERROR Room in The Void allows Isaac to reset the floor, so teleport items like Undefined can let Isaac repeat The Void multiple times.
• Defeating a final boss in The Void that is not Delirium will not give you a Completion Mark of that boss and will not unlock the respective item.
• Using the debug console to teleport to the boss room will not work, as the game doesn't know which room to send you to, so it will simply not do anything.

Bugs

Bug! Occasionally Isaac is unable to enter the portal. Sometimes this can be fixed by walking as far away as possible, waiting a few seconds, then slowly edging into the portal, or putting 1-2 bombs into portal.

Boss

Delirium

This floor contains multiple boss rooms, only one of which will contain Delirium. The other boss rooms contain previous bosses, including "final" bosses such as ??? or The Lamb, but not Mega Satan. Items dropped in The Void can drop from any item pool.

Notes

• Even though it is indicated as a 1x1 room on the map, Delirium's room is a 2x2 room and is generated on the map as a 2x2 boss room. As such, the 2x2 room that contains Delirium can only be adjacent to a single non-boss room on The Void.

Thus, if Isaac sees a boss room and if every 2x2 room that could be placed on top of the 1x1 boss room icon on the map would have more than 1 connection with non-boss rooms on the map, this boss room cannot be Delirium's room. This generation rule allows Isaac to either safely enter certain boss rooms in order to gather items before fighting Delirium, or to not enter these boss rooms knowing that Delirium is not there.

Music

The music that plays in The Void is titled Terminus.

• The music appears to be a remix of boss themes, Genesis 22:10 (title screen) and Burning Basement themes.

Trivia

• It is implied that the different forms (floors from Chapters 1 to 6) of this floor are just Isaac's hallucinations, as the Void's icon on the progress bar (after advancing to the next floor) is a red vortex, and the "floor" graphic (below the player character and bosses in "VS" screens) is red as well.
• On Isaac's last will, The Void is referred to as "some dying memory".
• Occasionally, there will be a static distortion and the background and objects of the room may change to those of other chapters.
• Mom's Heart can still spawn as a boss, even if it is replaced with It Lives on a normal playthrough.
• In Afterbirth+, The Void is the only floor that can be cleared indefinitely with Undefined.

Gallery

• 

  The red "floor" of the Void, featuring Apollyon

• 

  The Void's icon on the "Progress Bar". Note the vortex in the middle.