Use the following codes as your profile name to unlock the corresponding secret function:
Brutal Difficulty: BRUTAL
To Die fast: DBLDAY
To Aim better: DEADAIM
Get Better Defense: ERINROBERTS
Get Cartoon Mode: HVYMTL
Tougher Characters: MATTSOELL
Rapid Fire Weapons: RAPIDFIRE
Unlock Stupid AI: SPRAGNT
Unlock all Characters: GARNER
Unlock all Mission Maps: VENGAR
New Brutus appearance: GARVEN