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 Team
Sonic Team has developed a number of video games, with many of them becoming bestsellers. The studio is best known for its "Sonic the Hedgehog" series of platform games, which account for the majority of Sonic Team's work; the 1991 release of "Sonic the Hedgehog" is considered one of the most important moments in video game history, as it propelled Genesis sales and displaced Nintendo as the leading video game company. Sonic Team have also developed a wide variety of other games, including action games such as "Nights into Dreams", "Burning Rangers", and "Billy Hatcher and the Giant Egg," the online puzzle game "ChuChu Rocket!", the online role-playing game "Phantasy Star Online," and the music game "Samba de Amigo". "Phantasy Star Online" is credited for introducing online RPGs to consoles and was the first online RPG for many players. According to Sean Smith of "Retro Gamer", few companies could claim to have released as many AAA games over such a long period, especially between 1991 and 2000. Some Sonic Team games, such as the original "Sonic" games for the Genesis and "Nights", are considered some of the best video games ever made.