It was a robotic copy of Sonic the Hedgehog created by Dr. Eggman. It served as the first line of defense aboard the Death Egg during the West Side Island incident.

Sonic encountered Mecha Sonic in a large hall right after succeeding in entering the Death Egg. After landing on the other side of the room, Mecha Sonic began having a one-on-one fight with the blue hedgehog, while Dr. Eggman followed the battle from a small hole in the wall. However, Sonic defeated Mecha Sonic.