At the title screen, press Up, Up, Down, Down, Left, Left, Right, Right, Select. If you entered the code correctly, the word "Start" will turn to "Animation".
Debug Mode
At the title screen, press R1, R1, L1, L1, R2, R2, L2, L2, Left, Circle, Right, Square, Select, Start. Now full equipment will be available during the game. Press Select to skip the current level.
Door Passwords
On the fifth level, there is a door that requires a code. The code 6178 is written on the key that can be found in the previous room. On the ninth level, a code is also required. Enter 2360 at the upside-down triangle in the center of the level. Then, the exit will appear on its back.