Duality

Duality is an unlockable passive item added in The Binding of Isaac: Afterbirth †.

Effects

 * Whenever a Devil/Angel Room spawns after defeating a boss, the other will also spawn.
 * Upon entering one, the other one will disappear.
 * In rooms with only two accessible walls, only one of the two will spawn.

Synergies

 * : Time can be reversed while inside one deal to go into another.

Trivia

 * Duality is one of only five items to appear in both the Angel and Devil item pools, the others being, , and.
 * The Duality image appears to be similar in concept to the yin and yang symbol of Ancient Chinese philosophy, as the latter represents the concept of dualism as well. However, they don't quite appear to be exact in terms of the diameter format.