At memory card check, press L2, L2, L2, R2, R2, R2. The words 'Dels level skip on' will appear to bring up a level skip.
Invincibility and All items:
Pause the game and press L2, R2, L2 3 times, R2 3 times, Circle, Triangle, Square, Circle, Triangle, Square. If you entered the code correctly, you will hear a chime and the ninja will turn into a skeleton. Now you will be invincible with infinite items and lives. Repeat the code to turn back into the ninja while keeping the extra items.
Pause the game and press R2 3 times, L2 3 times, R2 3 times, L2 6 times. Now resume the game to have a new weapon. Repeat the code for a different weapon.
Decrease Boss Energy:
Pause the game while fighting against a boss and press L2 3 times, R2 3 times, and Triangle 6 times to dramatically reduce the bosses energy level.
When "Start" flashes, press L2 3 times, select 3 times, and R2 3 times
Get The Sword:
At the main menu, press Left, Right, Right, Up, X, X, Square and you should get the sword.