Beat the game once, and these codes will unlock. To make them work, go to the pause menu, hold all of the shoulder buttons (R1, R2, L1, L2), then press the buttons listed below to activate the corresponding cheat:

Invulnerability - SQUARE, CIRCLE, SQUARE, DOWN
Restore Health - SQUARE, SQUARE, CIRCLE, CIRCLE
All Upgrades - DOWN, UP, TRIANGLE, SQUARE
Infinite Missiles - SQUARE, SQUARE, UP, CIRCLE
Always Devastating - TRIANGLE, DOWN, TRIANGLE, UP
Perfect Mode - CIRCLE, UP, TRIANGLE, X (alternate code - CIRCLE, UP, TRIANGLE, DOWN)
Targeting Indicator Mode - UP, CIRCLE, DOWN, SQUARE
Unlock Level 4 Abilities for Gandalf - TRIANGLE, UP, SQUARE, X