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.
Knuckles' Chaotix
Development of "Knuckles' Chaotix" began in early 1994 as an engine test for the Sega Genesis dubbed "Sonic Crackers". Although Sonic Team is sometimes credited for developing the game, it was developed by another internal Sega development team including young members of the staff who had worked on "Sonic CD" (1993). Developed as an idea for the next "Sonic" game, the prototype featured Sonic and Tails joined together by an elastic band of energy. Development eventually moved to the more powerful 32X add-on for the Genesis. Sonic and Tails were replaced by a group of characters led by Knuckles the Echidna, but the core tethering gameplay was retained. The project was titled "Knuckles' Ringstar", and later "Knuckles' Chaotix". The "Sonic Crackers" prototype ROM image was later leaked online and can be played with emulators.