Unlock everything:
At the Main Menu, hold L and press A, X, Y, B, A, X, Y, B.

Unlock Cheat Menu
At the main menu, hold L and press A, Y, A, Y, B. The cheat menu will be unlocked in the options screen.

Unlock Cheats:
First unlock the cheat menu, then create a wrestler with the names below to unlock the cheat. Once unlocked, go to the cheat menu to toggle the cheats on or off.

Name	Effect
pstapley	Toon Characters
mbilodeau	Toon Background
rtaylor	Big Heads
okendall	Big Hands
tpiperi	Big Feet
jgintu	Halo
pjefferies	Ghost
ksimeonov	Greyscale
ewilliams	Wireframe
edma	First Person Camera
jche	Player 1 Invulnerable
cbarlow	Player 2 Invulnerable
ddaniels	Player 1 Unlimited Supers
jmaxwell	Player 2 Unlimited Supers
aiton	Hardcore Difficulty

Thanks to Revolution reader bennyboy753 and Magnum_Prime!