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.
- There is no Sega Logo in the beginning.
- 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.
- There are 2 invincibility stars in the prototype. The final Game Gear version has 4 stars.
- Sonic's sprites are exactly close to the ones from the Master System version.
- The map layout is slightly different than any version.
- The "GAME OVER" screen is garbled.
- The mountain range has a different hue, which resembles more to the hue from the Master System version.