Change The Character:
During gameplay you an press the select button and then highlight the Select button. Now enter:
L2, L1, L2, SQUARE, CIRCLE, SQUARE, L2, L2, L2, L2

Do not move your cursor, yet. You can hit the L2 button until you've selected your character.

One Shot One Kill:
During gameplay you an press the select button and then highlight the Select button. Now enter:
L2, L1, L2, SQUARE, CIRCLE, SQUARE, L3, R3, CIRCLE, SQUARE.

You'll hear a sound if you entered the code correctly

Unlimited Health:
During gameplay you an press the select button and then highlight the Select button. Now enter:

L2, L1, L2, SQUARE, CIRCLE SQUARE, R3, L3, R3, CIRCLE.

You'll hear a sound if you entered the code correctly

Extra Powerful Punches And Kicks:
During gameplay you an press the select button and then highlight the Select button. Now enter:

L2, L1, L2, Square, Circle, Square, R3, L3, Circle, Square

You'll hear a sound if you entered the code correctly. Now when you punch and kick an enemy they'll go flyin'.

Itty Bitty Characters:
During gameplay you an press the select button and then highlight the Select button. Now enter:

L2, L1, L2, SQUARE, CIRCLE, SQUARE, L3, R3, SQUARE, CIRCLE

You'll hear a sound if you entered the code correctly

Unlimited Phase Cloak:
During gameplay you an press the select button and then highlight the Select button. Now enter:
L2, L1, L2, Square, Circle, Square, L1, R3, L2, L3

You'll hear a sound if you entered the code correctly. Now you can stay Invisible for as long as you want.

Big Head Mode:
During gameplay you an press the select button and then highlight the Select button. Now enter:

L2, L1, L2, SQUARE, CIRCLE, SQUARE, START, SQUARE, CIRCLE, START.

You'll hear a sound if you entered the code correctly

Godly Guns:
During gameplay you an press the select button and then highlight the Select button. Now enter:
L2, L1, L2, Square, Circle, Square, L2, L2, L1, L3

You'll hear a sound if you entered the code correctly. This code will give you Unlimited Ammo and you'll never have to reload.

Huge Characters:
During gameplay you an press the select button and then highlight the Select button. Now enter:

L2, L1, L2, SQUARE, CIRCLE, SQUARE, R3, SQUARE, CIRCLE, L3.

You'll hear a sound if you entered the code correctly

Avoid Fall Damage:
When you fall from high area you take damage. When you near the ground push L2 to do a flip. This will eliminate damage.

Hard Mode:
During gameplay you an press the select button and then highlight the Select button. Now enter:
L2, L1, L2, SQUARE, CIRCLE, SQUARE, R3, L3, CIRCLE, SQUARE

You'll hear a sound if you entered the code correctly