Start a game. Pause the game then quit. Go down to replay level and click on bonus features entry. This screen is where you can enter codes.

Hidden Level:
Triangle, X, Trianle, X, Circle, Square, Triangle, Circle, X.

Infinite Ammo:
X, Triangle, X, Square, Circle, Triangle, Square, Triangle.

Infinite Lives:
Circle, Circle, Triangle, Circle, X, Square, Square, X.

God Mode:
Triangle, X, Circle, Circle, X, Square, Square, X.

All Guns:
Circle, Square, Circle, X, X, Triangle, Triangle, Square.

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Hints

All Weapons:
Beat the game.

Bonus Level:
Beat the game with at least a 50%.

Unlimited Ammunition:
Beat the game with at least a 55%.

Unlimited Lives:
Finish the game with at least a 60% completion.

Unlimited Health:
Finish the game with at least a 65% completion.

All Cheats:
Finish the game with a 78% completion.

Mummy Returns Trailer:
Beat the game and the Mummy Returns trailer will be unlocked.

Thanks to Revolution readers Unknown, tony and The Temple Of Bastet!