Entry location: Press start during the game, then enter the code
Scott Mitchell Invincible = Hold LT+RT+Back then press Y, Y, X, RB, X, LB
Team Invincible = Hold LT+RT+Back then press X, X, Y, RB, Y, LB
Unlimited Ammo = Hold LT+RT+Back then press RB, RB, LB, X, LB, Y
Put Your Life At 100% = Hold LT+RT+Back then press LB, LB, RB, X, RB, Y
You will then hear a chime to verify that your cheat was activated.
ed. note: Codes must be entered quickly. If you make a mistake, you may need to unpause the game, then pause again to clear the bad entry. It has also been reported that rather than holding LT, RT, and Back they can be pushed in sequence.