Mecha Sonic

Mecha Sonic is a stronger, more powerful robotic duplicate of Sonic the Hedgehog than Metal Sonic created by Dr. Eggman. Mecha Sonic appeared first and only in Sonic 3 and Knuckles, as a major boss in Sonic's story, and the final boss in Knuckles' story. However, Mecha Sonic is now a very popular villain in fandom. He appears in Super Mario Bros. Z, as the main antagonist of the first saga, where he is searching for the Chaos Emeralds so he can reach his ultimate form, Metallix.

Mario and Sonic: Worlds in Danger
Mecha Sonic appears as a major villain in Jmkrebs30's Flash series Mario and Sonic Worlds In Danger, alongside Basilisx. He is one of Bowser and Dr. Eggman's secret soldiers and will be unleashed along with Basilisx and Metal Sonic later on in the series. It has been confirmed that He and Basilisx will fight Mario and Sonic aboard the Death Egg near the end of the series. It's also shown in the second intro that Mecha Sonic can fuse with Metal Sonic to become Metallix.