At the player selection screen, hold L1 + R2 + Up + Square and press Circle. If you entered the code correctly, you will hear the sound of a bouncing ball.
Play as Mr. Tonkin
At the player selection screen, press L2(2), R1(3), Down, Triangle(4), Circle. If you entered the code correctly, you will hear a shout.
Play as Mattox
At the Player Select screen, press L2, L2, R1, R1, R1, Down, Triangle, Triangle, Triangle, Triangle, X. You should hear a ball bounce.
Play as Adversa
At the Player Select screen hold L1, R2, Up, Square, X. You should hear a ball bounce.