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
The first "Sonic the Hedgehog" game, released in 1991, was conceived by Sega's Sonic Team division after Sega requested a mascot character to compete with Nintendo's mascot Mario. Its success spawned many sequels and helped Sega become one of the leading video game companies during the 16-bit era of the early 1990s. The first major 3D "Sonic" game, "Sonic Adventure", was released in 1998. Spin-offs have explored other genres, including racing games such as "Sonic R" (1997) and sports games such as "Mario & Sonic at the Olympic Games" (2007).