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 CD
The Sega CD's flagship game, "Sonic CD" was conceived as an enhanced port of "Sonic the Hedgehog 2", but was reworked after lackluster sales of "Sonic 2" in Japan. Sonic co-creator Naoto Ohshima directed and Sega developers designed the game to show off the technical capabilities of the Sega CD. The game features the debuts of Amy Rose and Metal Sonic, and includes animated cutscenes produced by Toei Animation. Two soundtracks were composed for the game: the original score was composed by Naofumi Hataya and Masafumi Ogata, while the North American score was composed by members of Sega Technical Institute.