Mecha Sonic (Originally know as Metal Sonic) is a robot created by Dr. Eggman for the sole purpose of destroying Sonic. He serves as the primary antagonist for the first saga of Super Mario Bros Z. After Metal Sonic was created, he fought Sonic in their first battle, and lost. However, he returned faster and more powerful than ever, but was still beaten. Meanwhile, Metal Sonic sneaked into the Death Egg, combined with all of the other Sonic robots, and transformed into the almighty Mecha Sonic. As Dr. Eggman entered and threatened to deactivate Mecha Sonic for his disobedience, Mecha Sonic causes the Death Egg to crash into Mobius with Eggman on it. After destroying the Death Egg, Mecha Sonic decided to search for the 7 Chaos Emeralds while killing Sonic's friends in the process. He kills Tails, Amy, Knuckles, Cream, Cheese, and presumably Rouge and Omega. Mecha Sonic collected six Chaos Emeralds while Sonic had the seventh emerald. He found Sonic, easily defeated him, and got the last Chaos Emerald. Before Mecha Sonic can transform into his ultimate form, Shadow used Chaos Control to send the Chaos Emeralds to a different dimension. Before Sonic and Shadow could fight the robotic tyrant, Mecha Sonic used Chaos Control that he had absorbed some of their power to teleport to where the Chaos Emeralds were, thus leaving Sonic and Shadow behind with no way of pursuing him.
The picture above is a 3D model of Mecha Sonic but his sprite can be seen below and the image for the forum is locked on the homepage of the site. Mecha Sonic has also appeared in Sonic 3 & Knuckles as the last boss that Knuckles must face while he switches between his normal and super state by using the power of the Master Emerald.
An image of Mecha Sonic facing against Knuckles in his ultimate state.
Here you may feel free to discuss about Mecha Sonic and if he would be an success in the video game series of Sonic in the future.