Play As the Enemy:
Highlight the Game Start option on the main menu. Then sweep the D-pad in a counter-clockwise half circle starting from right and then press Triangle. The Game Start option will turn red if entered successfully. Select Game Start to get a menu that will allow all bosses and some enemies to be selected.

Versus Mode:
Sweep the D-pad in a Full-Circle at the main menu and then press X, Square, Circle, Triangle. You will hear a sound if done successfully. A versus mode option will be now be possible.

Extreme Difficulty:
Highlight the Game Start selection on the main menu. Hold Left for three seconds and then press right. next, press circle, triangle. The Option selection will turn red if you were successfuly. Go to the option menu to change the difficulty setting to extra hard