Backasswards is an unlockable challenge in The Binding of Isaac, added in the Afterbirth+ DLC.

This page shows the latest information as of the new Repentance+ (Online Co-op) DLC.
To see information about this challenge for the previous Repentance version, check this page instead.

Key Piece 1
Key Piece 2
8-10 random items

Note: this list does not include characters' default starting items.

The challenge starts from the Mega Satan fight, and the floors are in reverse order.
Isaac loses a heart container on every floor, as well as the oldest item in his inventory.
Every floor starts with a boss fight and ends with a beam of light in the starting room.

Based on the rules set in the .xml file, the following special rooms are disabled during this challenge:

Based on the rules set in the .xml file, the following curses are always enabled or cannot be encountered:

Note: curses not listed here behave normally unless otherwise mentioned in the additional notes.

The following is unlocked for completing the Backasswards challenge: Lazarus starts with Anemic.

Defeat Mega Satan and unlock The Negative.

• Check out the challenge description on the external Isaac Wiki.