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 (1991 video game)
"Sonic the Hedgehog" has been available for all three major seventh-generation video game consoles. It was part of the Wii Virtual Console at the service's 2006 introduction, and was released for the Xbox Live Arcade and PlayStation Network shortly afterwards. The game was released for the iPod Classic, iPod video, and video-capable iPod Nano models in 2007 and for Apple's iOS in April 2009. "Sonic the Hedgehog" became available on GameTap in September 2009. In October 2010, it was released on Microsoft Windows via Steam. The game was ported to Android and released in December 2012. Additionally, it is an unlockable reward in the console versions of "Sonic Generations". It was also made available on the Sega Forever service on iOS and Android in June 2017. A port for Nintendo Switch was released on September 20, 2018 as part of the Sega Ages line of rereleases. It adds features including the ability to use moves from "Sonic 2" and "Sonic Mania", a challenge mode, a time attack for the first stage, and features from the 3DS rereleases of the game and its sequel.