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 Saturn
Like the Genesis, the Saturn had an Internet-based gaming service. The Sega NetLink was a 28.8k modem that fit into the cartridge slot in the Saturn for direct dial multiplayer. In Japan, a now defunct pay-to-play service was used. It could also be used for web browsing, sending email, and online chat. Because the NetLink was released before the Saturn keyboard, Sega produced a series of CDs containing hundreds of website addresses so that Saturn owners could browse with the joypad. The NetLink functioned with five games: "Daytona USA", "Duke Nukem 3D", "Saturn Bomberman", "Sega Rally", and "". In 1995 Sega announced it was developing a variant of the Saturn featuring a built-in NetLink modem under the code name "Sega Pluto", but it was never released.