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.
Sega Genesis
In its first foray into online gaming, Sega created Sega Meganet, which debuted in Japan on November 3, 1990. Operating through a cartridge and a peripheral called the "Mega Modem," this allowed Mega Drive players to play a total of seventeen games online. A North American version, dubbed "Tele-Genesis," was announced but never released. Another phone-based system, the Mega Anser, turned the Japanese Mega Drive into an online banking terminal.