Metal Sonic
From Sonic - NeoWiki
Metal Sonic (Sonic CD version)
The original Metal Sonic was created by Dr. Robotnik. Its job was to kidnap Amy Rose the Rascal, as to lure Sonic into a trap. Metal Sonic was believed to be deactivated in a race on Stardust Speedway. Its next major plot line was in Sonic Heroes, where it creates a robotic Dr. Eggman to lure Team Sonic into another trap. This version of Metal Sonic believes it is the true Sonic, or that it is better than the real Sonic (an superiority complex).
Metal Sonic has a cameo part in Sonic Adventure, in a flashback with Amy and Sonic, and also appears as a playable character in the 2 player mode of Sonic Adventure 2, as well as being the final boss character in the arcade game, Sonic the Fighters.
Silver Sonic
Silver Sonic appeared in both 8-bit and 16-bit incarnations of Sonic The Hedgehog 2. In the Megadrive version, Sonic faced off this shoddy badnik at the top of the Death Egg, before he faced off against the final boss (a towering robot version of Eggman). It's 8-bit counterpart is far more powerful, and has a far more advanced moveset; in the game, Sonic cannot spindash, yet this robot version can.






