At the main menu, select the "Extras" option, then choose the "Cheat Codes" option. There are four boxes with pictures in them. Line up the pictures in the correct order by scrolling through them, then choose "Enter Code" to activate the code.

Invincibility

Enter Baseball, Baseball, Baseball, Shirt as a code.

Big hair

Enter Baseball, Bat, Bat, Baseball as a code.

Big head

Enter Hat, Helmet, Helmet, Hat as a code.

Big feet

Enter Hat, Glove, Glove, Hat as a code.

Sunglasses

Enter Glove, Glove, Helmet, Helmet as a code.

Paper pants

Enter Bat, Bat, Hat, Hat as a code.

Underwear

Enter Hat, Hat, Shirt, Shirt as a code.