Sonic the Hedgehog Pocket Adventure
In August 1999, SNK announced that they were collaborating with Sega to develop a "Sonic the Hedgehog" game for their Neo Geo Pocket Color handheld system. The game was developed by SNK, with supervision from Yuji Naka and Sonic Team at Sega. This marked the first time Sega was directly involved in the development of a "Sonic" game for a non-Sega platform. The team planned for "Sonic Pocket Adventure" to be a return to the classic 2D gameplay style found in the "Sonic" games on the Sega Genesis. In particular, many game design and visual elements are borrowed from "Sonic 2". The game's background music tracks are also 8-bit renditions of music from "Sonic 3". "Sonic Pocket Adventure" was released first in North America on December 4, 1999. SNK released a system bundle with the game included for the holiday season. The game was released in Japan two weeks later, and in Europe in February 2000.
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.