Binding of Isaac: Rebirth Wiki
Character Isaac appearance.png
Full red heartFull red heartFull red heart
Table dividing line 1.png
Challenge Number
Available Rooms
Item Pool Treasure Room.png: yes          Item Pool Shop.png: yes
Boss Mom's Heart portrait.png
Gold Heart Gold Heart
Unlock Method


Added in Afterbirth

XXXXXXXXL is Challenge #21. This challenge changes all floors to be the size of XL Womb but does not combine the floors of each chapter. The goal is to defeat Mom's Heart Mom's Heart/ It Lives It Lives. Alternatively, you can defeat The Lamb The Lamb by teleporting to Dark Room Dark Room via a Sacrifice Room Sacrifice Room, or Added in Afterbirth † Delirium Delirium if the portal to The Void The Void appears after defeating Mom Mom.

  • Added in Repentance Teleporting to the Dark Room Dark Room via a Sacrifice Room Sacrifice Room is no longer possible, since the challenge does not end in the Dark Room.


Due to the floors being much bigger, it makes important rooms like Treasure Rooms and Shops take significantly longer to find, which can make the run difficult if Isaac has rather weak items. It also makes Secret and Super Secret Rooms much harder to find. Although all floors are technically XL, there is only one treasure and boss room on each floor. On the plus side, since there are more rooms, there are more opportunities to generate pickup items.


  • Items and pickups that reveal the map are very crucial, allowing easy maneuvering between Special Rooms throughout floors.
  • Items that provide benefits based on clearing rooms, like Little C.H.A.D. Little C.H.A.D., will help Isaac significantly because of how many rooms he will go through in this challenge.
  • Teleportation cards, such as The Stars and The Hermit, are very valuable, as they allow easy access to Special Rooms. The Emperor is especially powerful, as it can be used to skip the entirety of a floor.
  • Avoid items that teleport Isaac at random, such as Cursed Skull Cursed Skull, as they can significantly slow down progress by potentially teleporting him to the other side of the map. Picking up the Cursed Eye Cursed Eye is not recommended for the same reasons.
  • Added in Repentance Planetariums are very useful for this challenge. Added in RepentanceSol Sol can be used to find the boss room, Added in RepentanceTerra Terra can break doors with ease, and Added in RepentanceMercurius Mercurius allows you to walk through rooms with ease. Considering you might skip an item room or two anyway in the interest of time, this can be a very effective way of completing the challenge.


  • Curse of the Labyrinth can still spawn as normal, combining the two floors as normal, and causing there to be two treasure rooms and boss rooms. The size is unchanged.
  • It is very rare to start next to a treasure room in this challenge.