Unlock Everything:
At the main menu Hold L and press Right, Right, Left, Left, Down, Up, B
Unlock Dark Phoenix:
Beat Arcade Mode using Phoenix
Unlock Bishop:
Beat Arcade Mode using Gambit
Unlock Psylocke:
Beat Arcade Mode using Betsy
Unlock Bastion:
Finish Story Mode using Magneto without losing any matches. You will fight Bastion. Defeat him to unlock him.
Unlock Blob:
Beat Arcade Mode using Bishop
Unlock Sentinel A:
Beat Arcade Mode using Cyclops
Unlock 3rd Costume:
Beat Story mode using any character
Unlock 6th Costume:
Beat 10 characters in time attack with any character in under 15 minutes
Unlock 7th Costume:
Use team mode and fight with 8 characters. Defeat the entire opponent team using 2 or more of your characters
End Sequences:
Magneto Victory Ending - Defeat Bastion using Magneto
Phoenix Victory Ending - If you lose the Magneto vs Bastion fight you can fight Phoenix vs Bastion
Secret Ending - Get a PERFECT victory in the Phoenix vs Bastion fight and you will unlock Dark Phoenix.