From Sonic Retro
Sonic eXtended Genesis, aka Sonic XG, is a game being created by Sir Euan and Nitemare, and has gone through many different variations in the past.
At one point in time, the fangame was going to be merged with Retro Sonic and Sonic Nexus in order to create Retro Sonic Nexus,a decision made in 2007, but is again being developed as a separate title.
Happening after the events of Sonic & Knuckles, Sonic falls from the atmosphere and lands on the tornado, carrying the Master Emerald. Suddenly, an object flies by striking the tornado with laser beams twice, plummeting Sonic to the Floating Island. It is revealed seconds later to be none other than Metal Sonic, who seen holding the Master Emerald, then flying off. In the background, a burning Death Egg is seen tumbling downwards, closer and closer, to the Floating Island....