In story mode, enter the following as your user name.

DEATHGAMER        - All Wrestlers and Arenas 
tpiperi           - Big Feet Mode 
okendall          - Big Hands Mode 
rtaylor           - Big Head Mode 
tho               - Big Head, Big Hands, and Big Feet mode 
mbilodeau         - Cartoon backgrounds 
pstapley          - Cartoon character 
edma              - First Person Camera mode 
pjefferies        - Ghost mode 
ksimeonov         - Greyscale mode 
jgintu            - Halo mode 
stomanovski       - Hardcore Al 
denicholas        - Invulnerable Players 
jche              - Player 1 Invulnerable 
ddaniels          - Player 1 unlimited supers 
cbarlow           - Player 2 Invulnerable 
jmaxwell          - Player 2 unlimited supers 
donttrythisathome - Unlock all cheats 
ewilliams         - Wireframe mode