Sonic the Hedgehog 3 introduced Metal Sonic in a credits scene to set up the character as a Sonic 4 villain, but it created a major problem.

Predating him by several years is Metal Sonic, a Sonic-resembling robot created by Dr. Eggman ... if they do so at all. Following Rush's storyline would probably be better for her as a character ...

It seems the same is true for [James Bruton]’s impressive Sonic the Self-Balancing ... wipe-outs and all. The knees of this robot are actuated using a pair of motors with ball screws, which ...