Seeing Double is an unlockable challenge in The Binding of Isaac, added in the Repentance DLC.
This page shows information as of the latest Repentance release.
To see latest up-to date information about this challenge for the new Repentance+ (Online Co-op) DLC, check this page instead.
20/20
20/20 (P2)
X-Ray Vision (P2)
Note: this list does not include characters' default starting items.
All enemies and bosses are doubled.
The following is unlocked for completing the Seeing Double challenge: Broken Glasses
Defeat Mother for the first time.