Rampage (Sega Master System)

Much like the arcade counterpart, you play as one of three monsters and destroy buildings.

Pretty damn good fun, if you ask me.

Unused FM Audio
For whatever reason, despite this port not being released in Japan (the only country whose Master System consoles contained the YM2413 FM chip), Rampage has code for FM music and sounds. The FM detection routines even occur at startup.

As such, it's possible to hear the FM sound in an export Master System with a custom FM board installed, a Japanese Master System with a region adapter, or simply an emulator which includes the YM2413 chip.

It is uncertain whether this port was planned for a Japanese release, but if not then why would FM audio be present?