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
While the prior game in the era continued the use of numerous playable characters and play styles, the following games would return to only have Sonic playable. "", an episodic high-definition 2D game akin to the 16-bit Sonic games, was developed for the PlayStation Network, Xbox Live Arcade, WiiWare. "" was released in 2012 for PlayStation Network, Xbox Live, Android, iOS, and Windows Phones. "Sonic Colors", a game for the Wii and Nintendo DS, was released in November 2010. It introduced a power-up system in the form of alien beings called "Wisps". "Sonic Generations" was developed by Sonic Team for Xbox 360, PlayStation 3, PC and Dimps for Nintendo 3DS which was released in November 2011, featuring both modern and classic interpretations of Sonic.