Restore health:
Pause the game, then hold L1 + R1 and press Down, Up, Right, Left, Down, Up, Square. If you entered the code correctly, you will hear a sound.
Restore stamina:
Pause the game, then hold L2 + R2 and press Right, Left, Right, Left, Down(2), Square. If you entered the code correctly, you will hear a sound.
Extra money:
Pause the game, then hold L1 + L2 and press Left, Left, Up, Down(2), Up, Square. If you entered the code correctly, you will hear a sound.
More store items:
Pause the game, then press L1, R1, L1, R1, R2(2), Triangle. If you entered the code correctly, you will hear a sound.
All characters:
Enter the character customization screen and highlight the "Name Selection" option. Quickly press L1, R1, R2, L2, L1, R1, R2, L2, Square. Press Left or Right to select a new character.
Hard Difficulty:
Finish the game on both Easy and Normal.
Or:
Get 1,000 points.
Sudden Death Mode:
Get 7,500 points to unlock Sudden Death Mode.
Very Hard Difficulty:
After unlocking Hard Mode, finish the game on Easy difficulty a number of times. In this mode, only 1 or 2 hits are needed to kill or be killed.
