The Magic Candle

Sound Test
Press and hold Up + Right + A + B on Controller 2 and Up + Right + A + B + Select + Start on Controller 1 at the same time, then press Reset.

Press Left / Right on Controller 1 to select music, and press Left / Right on Controller 2 to select a sound. Press A to restart music. Press any other button to return to the game.

The sound test also contains a build date, indicating that the game sat around for over seven months before release.