Sonic the Hedgehog
Due to the success of "Sonic" games on the Sega Genesis, the series was introduced to the Master System and the Game Gear. Sega began by releasing "Sonic the Hedgehog", a 2D platform game, in 1991. The game featured Sonic's ability to run and to jump at high speeds like its Mega Drive/Genesis counterpart but with notably different level design and music. Sega later released "Sonic the Hedgehog 2" another 2D platform game, in 1992. The game differed from its Genesis counterpart with different levels and music and by not including a "spin dash" maneuver. It also featured a different storyline in which Doctor Robotnik kidnaps Tails, who is non-playable in the Master System/Game Gear version. "Sonic Chaos"/"Sonic and Tails" (Japan), released in 1993, was similar to the earlier two Sega Master System/Game Gear "Sonic" games, but featured Tails as a playable character. A sequel, "Sonic Triple Trouble"/"Sonic and Tails 2" (Japan), a 2D platform game, was released in 1994 for the Game Gear and introduced a new character, Nack the Weasel, who, along with Knuckles and Doctor Robotnik, raced to collect the Chaos Emeralds. One of the last games for the Sega Game Gear, "Sonic Blast", was released in 1996 and featured prerendered sprites.
Ristar
Back in late 1994, Sega was originally pitching "Ristar" to be the successor of Sonic the Hedgehog. However, the game never received a ton of exposure or sales, mainly due to being released just three months prior to the Sega Saturn, Sega's successor to the Genesis, overshadowing it. In a 1994 "Electronic Gaming Monthly" interview, Sega marketing staff Lisa Best and Terry Tang claimed "Ristar" was not designed by the same "Sonic" programming team, although much of the game's staff would later go on to create "Nights Into Dreams" for the Saturn, the next game to be officially credited to Sonic Team. This, along with "Ristar's" inclusion in a number of "Sonic" themed compilations and re-releases in subsequent year, would lead game journalists to retroactively label the game as being developed by Sonic Team.