Press Y, A, B(2), A, Down, A, B(2), A at the title screen. The screen will flash to confirm correct code entry. Press Select during game play to advance to the next level.
Begin a new game and defeat the Mutant Birdman at the end of the first level. Hold A + B + Start before the screen fades. Release the buttons when the next level starts. The life meter should extend across the screen to confirm correct code entry. Note: This effect will be canceled if any life or mutation power-ups are picked up.