Mecha Sonic did not originate from fanon, and the information on this page may not be entirely accurate to their canon. You may read more about this subject in the context of their canon on the following wiki(s):
Mecha Sonic is a powerful robot built by Dr. Eggman that appeared in the game Sonic & Knuckles. He can roll into a ball and spin-dash just like his living counterpart. He can also float as a spiky ball and attack from above. His powerful transformation yet was Super Mecha Sonic.