Not a prototype, but a hard to dump game cart.
"CJ Elephant Fugitive for Game Gear, an elusive platformer published by Codemasters.
This game took a long time to reach the internet and is also latest licensed Game Gear that wasn't dumped and released so far! Modder extraordinaire Ichigobankai helped to get this dump done. Thank you :)"
Grab it here: http://www.smspower.org/forums/viewtopic.php?t=13857&sid=4a9ef7f2a4dab9f413d4f6f0baa375c4