Play as the Boss
At the main menu, hold L1 + R2 + Circle + Start for five seconds. Then, select single player mode and choose any character.
Submitted by Tyaka420
Bonus music
Play tracks 2 through 34 of the game disc in an audio CD player.
Submitted by Tyaka420
Last Level skip
On Level 2, go to the far left hand side of screen and hold: Down, Left, R1, L1 and start.