Mega Satan Arena is an unlockable room in The Binding of Isaac.

Found in the starting room of the Chest and Dark Room floors.

The Mega Satan Arena is a special Boss Room that features a fight against Mega Satan.

Unlocking the door requires and consumes both Key Piece 1 and Key Piece 2. It can, alternatively, be opened by an item such as Dad's Key.

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

Defeat ??? or The Lamb.

The Mega Satan Arena is associated with the Boss item pool. Items that spawn in this room will be selected from the associated item pool.

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