Debug mode:
Pause game play, then hold L2 and press Left, Up(2), Triangle, Right, Square, Left, Triangle, Up, Down, Right(2). This will unlock all levels in the game.

Invincibility:
Pause game play, then hold L2 and press Right(2), Left, Triangle, X, Up, Circle, Left.

Unlimited Spirit Spells when acquired:
Pause the game, then hold R2 and press Left, Triangle, Left(2), Circle, Left, Triangle, Right, Circle, Up(2), Down.