The recent Sonic 2 GG autodemo made me think of this old prototype of Sonic 1, released IIRC by 2004: http://info.sonicretro.org/Sonic_the_Hedgehog_%28Game_Gear_prototype%29 Since it is commented the Game Gear port of Sonic 1 is based off the SMS version, my curiosity took me to use the SMS PAR Codes in this early GG Proto. The result is that I can access some deleted / garbled data, which will sometimes reset the game, or display black / blue screens, or in the best case take you inside the level. Some places are pretty recognizable, even with the garbled tiles and objects. Some are not recognizable and may produce some strange effects as causing Sonic to be unable to jump or to be stuck in his rolling pose, life monitors being carried away, strange platform structures, and a completely f***** up try to the ending sequence. As I don't have much time to describe better all the sequences of this video, it is being provided as is. Well, it is pretty easy to try it on any emulator using the PAR codes listed here: http://info.sonicretro.org/Cheat_Codes:Sonic_the_Hedgehog_%288-bit%29 EDIT: Trying to embed YT video. There's also a brief description at the video page.