Various Cheats
Enter any of the following codes at the "Press Start" title screen. Visible confirmation will be given when a code is entered correctly.

Platinum unlock (all boxers, arenas, game modes, etc.): Square, Circle, L2, R2

Additional custom boxer textures (brow styles, tattoos, etc.): L1, R1, X, X, Triangle, X

Big head mode: Square, Circle, Up, Down

Small head mode: Square, Circle, Down, Up

2D/flat mode: Down, Up, Circle, Square

Super mutant mode (characters grow and shrink randomly): Square, Left, Up, Triangle

http://www.playstationpro2.com