The Sonic the Hedgehog Game Gear prototype is a one level demo version of Sonic the Hedgehog for the Sega Game Gear. It was compiled to demonstrate the Game Gear port to the gaming press. The process of porting the game from the Master System version is incomplete, which is evident for a number of reasons.
- There is no Sega Logo in the beginning, just like the Master System version.
- Sonic is placed further right at level startup.
- Sonic's palette changes to a darker blue when passing the end level sign.
- A strange strip appears at the top of the level briefly, probably a glitch as touching it does nothing.
- The Invincibility stars are more similar to the Master System version. The final game has 4 stars.
- Sonic's sprite has not yet been finalized.
- The map layout is slightly different than any version.
- Game over screen is messed up due to some tile rearrangement.
- The mountain range has a similar hue to the Master System version.