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.
Educational games in the Sonic series
In 1996, Sega and Orion Interactive collaborated to produce "Sonic's Schoolhouse", an educational game in the Sega PC brand for Microsoft Windows. It was developed using a game engine similar to "Wolfenstein 3D"s and ten educators and psychologists helped create the game's challenges. A cartoon clock was originally the star of the game but was replaced with Sonic; thus, "Sonic's Schoolhouse" is only tenuously connected to the rest of the franchise. The game was released as part of Sega's 20 million "Blue is Back" marketing campaign to promote six "Sonic" games releasing in the holiday shopping season; advertisements for the game were run in magazines and it was promoted in store displays. "Sonic's Schoolhouse" also came bundled coupons worth 40 in discounts for "Sonic" merchandise, including comics and plush toys.