Sonic the Hedgehog
The Sega Genesis had "add-on" systems that incorporated "Sonic" games. "Sonic CD", released for the Sega CD, was a 2D platform game released in 1993. The game introduced the characters Amy Rose and Metal Sonic and featured levels that differed depending upon whether Sonic was in the past, present, or future time frames. "Knuckles' Chaotix", a spin-off released in 1995 for the Sega 32X, featured Knuckles and a new group named Chaotix fighting against Dr. Robotnik. The game featured a two-player cooperative system in which the on-screen characters were connected by magic rings. There was also "Sonic Eraser", a puzzle game released exclusively on Sega Game Toshokan in 1991.
Sonic the Hedgehog (1991 video game)
A version of "Sonic the Hedgehog" was developed by Ancient and released in late 1991 for Sega's 8-bit consoles, the Master System and Game Gear. Its plot and gameplay mechanics are similar to the 16-bit version, though some level themes and digital assets are different and Chaos Emeralds are scattered throughout levels rather than special stages. Gameplay as a whole is simplified; the level design is flatter and has a larger focus on exploration, with no vertical loops, and Sonic cannot re-collect his rings after being hit. The game has a different soundtrack composed by Yuzo Koshiro, which includes adaptations of music from the original version. It was the final game released for the Master System in North America. The Master System version was re-released for Wii's Virtual Console service in North America and Europe in August 2008. The Game Gear version was re-released for the Nintendo 3DS Virtual Console on June 13, 2013, and included as an unlockable game in "" for GameCube and Windows and "Sonic Mega Collection Plus" for PlayStation 2, Xbox, and Windows.