Die enough times to get offered Easy mode

Kiss the Nyad

Collect all of the Muse Keys

Complete the Challenge of Atlas

Clear the airwaves

Defeat the Desert Sirens

Rescue the Oracle with 10 seconds to spare

100% Complete

Achieve 16 medals on predator challenges

Achieve 24 medals on combat challenges

Complete story mode on Hard difficulty

Perform a perfect combo including all of Batman's combat moves (any play mode)

Complete story mode on Easy difficulty