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.
Platform game
1990 marked the release of the Super NES, along with the eagerly anticipated "Super Mario World". In order to fend off the new competition, Sega released "Sonic the Hedgehog". Whereas Nintendo's offering featured a conservative design, true to the "Mario" tradition, "Sonic" showcased a new style of design made possible by a new generation of hardware. "Sonic" featured large stages that scrolled effortlessly in all directions, as well as all manner of uneven terrain, curved hills, and a complex physics system that allowed players to rush through its levels with well-placed jumps and rolls. Lastly, there was the game's eponymous main character. Sega decided to give Sonic a rebellious personality in order to appeal to older gamers, and super speed to help show off the "Genesis"' hardware capabilities. The game proved to be a massive hit, was a successful pack-in with new systems, and cemented the view that platform games would make or break a console.