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 the Hedgehog
Between "Sonic Advance 2" and "Sonic Advance 3", two other Sonic games were released: "Sonic Battle", a 3D fighting game, and "Sonic Pinball Party", a pinball simulation. The last Sonic game was released for the Game Boy Advance is "Sonic The Hedgehog Genesis" on 2006, which features the original Genesis game and the 15-anniversary mode with the Spin Dash.