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.
Sega
Sega released its next console, the Sega Genesis (known as the Mega Drive outside North America), in 1988. Although it was a distant third in Japan, the Genesis found major success after the release of "Sonic the Hedgehog" in 1991 and briefly outsold its main competitor, the Super Nintendo Entertainment System, in the U.S. However, later in the decade, Sega suffered commercial failures such as the 32X, Sega Saturn, and Dreamcast consoles. In 2001, Sega stopped manufacturing consoles to become a third-party developer and publisher, and was acquired by Sammy Corporation in 2004. In the years since the acquisition, Sega has been more profitable, but has been criticized for prioritizing quantity of game releases over quality.