Enable the "Unlimited Continues" code. When the HIGH SCORE screen appears, press RIGHT, UP, UP, LEFT, RIGHT, RIGHT, RIGHT, LEFT, DOWN, DOWN, RIGHT, UP. A third 'boom' confirms correct code entry.
To use it, press L during gameplay to jump to the next level.
At the title screen, quickly press Left, Up, Right, Up, Left, Left, Left, Right, Down, Down. A second boom confirms the code's activation. Press R at any time during game play to receive nine credits.