Use the following cheat combinations to enable the corresponding effect:
God Mode: up, down, left, right, up, down, left, right
Kill all enemies: A, B, Y, X, A, B, Y, X
No Fall: up, A, up, B, Y, up, X
Get all weapons: up, down, left, right, A, B
Kung Fu Fists: right, down, left, A
Get Minigun: up, up, down, down, A, B, A, B
Unlock All Levels: X, up, right, up, right