Complete the Arcade Mode with Gambit to unlock Bishop.
Complete the Arcade Mode as Bishop to unlock Blob.
Unlock Dark Phoenix
Complete Arcade mode with Phoenix to unlock Dark Phoenix.
Complete Arcade mode with Betsy to unlock Psylocke.
Whilw at the main menu press the following buttons:
Hold L1, then press RIGHT, RIGHT, LEFT, LEFT, DOWN, UP, CIRCLE.
Unlock New Costumes
Complete Arcade Mode with any character to unlock new costumes.