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"'s success led to an extensive media franchise, with the first of many sequels, "Sonic the Hedgehog 2," released the following year. It has generated dozens of additional games and a large cast of recurring characters, keeping Sonic and Robotnik (later renamed as Eggman) mainstays, and continued beyond Sega's exit from the console industry after the Dreamcast. The series has ventured from platformers to fighting, racing, role-playing, and sports games, and also expanded into anime, manga, cartoons comic books, novels, and toys. "Sonic the Hedgehog" is one of the best-selling video game franchises of all time, with over 140 million copies sold or downloaded worldwide across consoles, PC’s, mobile phones and tablets by May 2014. The first stage, Green Hill Zone, has been used in several games, such as "Sonic Adventure 2", "Sonic Generations", "Sonic Mania", "Sonic Forces", and the "Super Smash Bros." series.