Unlock Mode: Zombie Survival
At the Title Screen, enter the following to kick some zombie butt: Down, Up, Right, Down, Up, Right, Down, Up, Right, Right, Right.
On the title screen, enter X, Circle, X, Square, X, Circle, Circle to start knocking blood out of your enemies.
Unlock: Sound Test
On the Overworld screen, pause the game and go into the Score Ranking menu. From there, press L1, L1, R1, R1, L1, L1, L1, R1, R1, R1, L1, R1.
This will unlock the path to the radio station and allow you to mess around with the various music and sound effects in the game.
Enable Multiples Of The Same Character
Want to play as your favorite character buy a jerk friend of yours picks them all the time? On the Title Screen, press Down, R1, Up, L1, Triangle, Circle.
Enable: The Power Of Love
To use the 'Power Of Love' sword at the start of every level, enter the following at the title screen: Square, Square, Square, X, Circle, X, Triangle.