@shadowman44 Yep, SMS Power posted news about the prototype a couple of years ago, it should still be on the front page but may not be now... They say that there might be missing content/code compared to the final but not much else.

Besides this game was in development when Sega suddenly cancelled a lot of Japanese releases ready for 1989 (California Games, Wonder Boy 3: The Dragon's Trap, Altered Beast, Galaxy Force, Shanghai [even has Japanese text during the attract mode when played on a JPN console], Rampage, Scramble Spirits [a prototype even had the 1989 year rather than 1988 of the final], Golfamania, Tennis Ace, Out Run 3D, Battle Out Run, Cloud Master, Vigilante, Rambo 3, Rastan, Rescue Mission, Time Soldiers, Ultima 4, the heavily delayed Summer Games and a few more), these feature FM music and may feature Sega logos. I don't know if Sega had plans for an US/PAL FM enabled Master System 2 otherwise why would so many games have music that cannot be heard and why games from 1990 onwards mostly have no FM at all (outside of Assault City where apparently two songs were coded and the eventual release of Summer Games). Some like Double Hawk, Battle Out Run and this game, the FM sound is hidden in the code. The proto cartridge that this got dumped is Western type though...

@shadowman44 Maybe it was after the possible race game that was never made

Dynamite Dux had a prototype? Whaaaaaat?