At the "Takara" logo press Down, Down-Left, Left, Down-Left, Down, Down-Forward, Right + Y. A sound will confirm the code. When you pick your character hold Start then hold B. Release Start and tap the control pad in any direction. All characters will change color, including the bosses.

When the game ends and the count-down screen appears, hold Up and press A + B + C to add one to your credits. You can only go to nine, but this trick may be repeated as often as needed

This cheat enable you to be one of the four bosses, Billy, Axel, Blood and Krauser in one-player mode. Start a game in one-player mode. Then press Down + Start. Then you will see Billy. Then press Right to be Axel, press Right again to be Blood and Right again to become the ultimate boss, Wolfgang Krauser.