Sonic Fighters

Sonic Fighters is a cancelled third-party Sonic game that was in production since 2003, meant to be a successor to the arcade title Sonic the Fighters.

In spite of being a third-party project, done as a collaboration between Quarantine Development and Paradox Development, a few Sonic Team programers had some involvement in the game as well.

The game has remained lost for years until turning up on an XBOX development kit.

Development
The game was originally started by Quarantine Development, who had no intent of showing it to SEGA until they felt it was ready. They brought on Paradox Development to aid in developing the game, namely creating a new fighting engine since Quarantine's was no longer up to date and to hasten development time at a more efficient pace. The game was close to getting full approval from SEGA, with most Sonic Team devs aiding on the project and Yugi Naka giving his approval. It was set to be released in 2004, but was promptly cancelled due to numerous factors such as Paradox becoming a part of Midway Games, other SEGA representatives outright rejecting the game and internal conflict between Quarantine and other Sonic Team programers.