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 Spinball
The game was developed by the American staff of Sega Technical Institute, as the Japanese staff was occupied with developing "Sonic the Hedgehog 3" and "Sonic & Knuckles". When Sega management realized that "Sonic 3" would not be completed in time for the 1993 holiday shopping season, they commissioned another "Sonic" game that would be. The game was hastily designed amid time constraints, with most work taking place over two months. "Sonic Spinball" was released for the Sega Genesis in November 1993, and for the Game Gear and Master System in 1994 and 1995, respectively.