While you are playing the game, press and hold L1 + R1 + R2 + Select, and enter X, Circle, Square, Triangle, X, Circle, Square, Triangle. Do it every time you want to skip levels.
Pause the game
If you press Start during the game, the AI can still frag you. But if you press Quit, the game will pause itself and it will ask you if you want to quit or not. TO continue just press "NO."
New Arena and two new players
Beat the whole campaign mode on "I Can Win." After the credits you will see two secret characters and a bonus level. Frag both of the characters to receive them as playable and also get the bonus arena.