Quickly press Up, Down, Left, Right, A, B during game play.
Farm: Easy kills
At the beginning of the game, Jack notices a stranger standing in his yard.. The game will instruct you to go out and confront him. Instead, go upstairs to the attic and find your .22 rifle. The zombie will start to bash his way into your house, but it is better than running up to him unarmed, as he will almost always bite you. Also, the key to the shed in your backyard is in the basement. If you go downstairs before coming into contact with the zombies, you can get a revolver, ammo, and a hammer from the shed. These make it a lot easier to fight off the walking dead at your house, and you can complete the level twice as fast.
God mode
Quickly press Up, Down, Left, Right, Up, Down, Left, Right during game play.
Invisibility
Quickly press X, B, A, B during game play.
Kill all spawned enemies
Quickly press A, B, Y, X, A, B, Y, X during game play.
Kung Fu fists
Find and read the "Day of the Kungfu Zombies" books in various levels. When you look at this book, it will not highlight an action response. You must search for the book, then press Action to read it. Your character will say "I know Kung Fu?", then a tattoo will appear on your hands. Your hands will now be stronger, and can kill zombies.
Alternately, quickly press Right, Down, Left, A during game play.
Level select
Quickly press X, Up, Right, Up, Right during game play.
Minigun
Quickly press Up(2), Down(2), A, B, A, B during game play.
No knock downs
Quickly press Up, A, Up, B, Y, Up, X during game play.