Invincibility:
Pause the game then hold L2 or R2 and press:
right, right, left, triangle, X, up, circle, left

Unlimited Spirit Spells after Learning Them:
Pause game then press and hold L2 or R2 and press:
left, triangle, left, left, circle, left, triangle, right, circle, up, up, down

Debug Menu:
Pause game then press and hold L2 or R2 and press:
left, up, up, triangle, right, square, left, triangle, up, down, right, right