Sonic the Hedgehog Megamix (commonly shortened to Sonic Megamix or Sonic 1 Megamix) is a 2005 overhaul ROM hack of 1991's Sonic the Hedgehog for the Sega Genesis, developed by Team Megamix the game was first initially released on May 31, 2005, as part of the 2005 Sonic Hacking Contest, with updates in the following years.