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 (2006 video game)
To celebrate the "Sonic" franchise's 20th anniversary in 2011, Sega released "Sonic Generations", which remade aspects of past "Sonic" games. The PlayStation 3, Xbox 360, and Windows versions feature a remake of "Sonic the Hedgehog"s "Crisis City" level, and every version, including the Nintendo 3DS version, includes a reimagined version of the boss battle with Silver. The decision to include "Sonic the Hedgehog" stages and bosses in "Sonic Generations" was criticized by critics and fans of the series; Jim Sterling of "Destructoid" referred to the Silver boss fight as the "catch" of the otherwise high-quality game.