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 Forces
"Sonic Forces" was announced alongside "Sonic Mania" under its codename during a twenty-fifth series anniversary event held by Sega at the San Diego Comic-Con on July 22, 2016. The presence of both Classic and Modern Sonic in the initial teaser trailer led some journalists to believe it was a sequel to "Sonic Generations", but Iizuka clarified that it was a separate game. The game was released worldwide on Microsoft Windows, Nintendo Switch, PlayStation 4, and Xbox One in November 2017. Prior to the game's launch, Sega released a four-part prequel comic written and drawn by Ian Flynn and Adam Bryce Thomas, who previously worked on Archie Comics' "Sonic the Hedgehog" series. A bonus edition was also released containing controller skins and downloadable clothing items for the Avatar based on other Sega games, such as "Jet Set Radio", "Puyo Puyo", and "Persona 5". A tie-in racing game for iOS and Android devices, "Sonic Forces: Speed Battle", was released in select regions in September 2017. After the game's release, several updates featuring new content were released, such as an in-game shirt for the Avatar featuring "Sanic", an internet meme of a poorly drawn Sonic, and the ability to transform into Super Sonic. The Super Sonic DLC was released for free, but was initially planned as paid DLC.