Unlock Everything:
At the Main Menu, hold L1 and press Right, Right, Left, Left, Down, Up, Circle.

Unlock Bastion:
Beat Story mode as Magneto without losing.

Unlock Bishop:
Beat Arcade mode as Gambit.

Unlock Blob:
Beat Arcade mode as Bishop.

Unlock Psylocke:
Beat Arcade mode as Betsy.

Unlock Dark Phoenix:
Beat Arcade mode as Phoenix or Story mode as Magneto.

Unlock Pyro:
Beat Arcade mode as Dark Phoenix on every difficulty level.

Unlock Sentinel A:
Beat Arcade mode as Cyclops.

Unlock Sentinel B:
Beat twenty consecutive opponents in Survival mode.

Extra costume 3:
Beat the game in Story mode to unlock a character's third costume.

Extra costume 4:
Beat twenty consecutive opponents in Survival mode.

Extra costume 5:
Beat Arcade mode on hard.

Extra costume 6:
Beat ten fighters in Time Attack mode in under fifteen minutes.

Extra costume 7:
In Team mode, set up an 8 vs 8 fight, and beat the other team using two characters max.

Extra costume 8:
Beat forty consecutive opponents in Survival mode.