To enable these cheats go to Team Management, then Customize, and change a player's name to one of the cheat codes list below then press enter (you should then hear a sound). Do that for all cheat codes, after which you can press back to undo the changes so that player's real name is not changed. Go back to the main menu. Press Scroll lock and a cheat menu will appear. Check the boxes next to the list of cheats to enable that cheat.

Kyle = Skeleton Players

Mr Hat = Crazy Ball

Powder = Silly Moves

Neila = Alien Model

Gabo = Big Heads

Cartman = Take a Dive

Gonzo = Hot Potato

Kenny = Flaming Ball

Zico = Enable WC Classics