Metal Knuckles

Metal Knuckles a robot version of Knuckles created by Dr. Robotnik. He first appeared in Sonic R as a unlockable character. He appeared in the Gameboy Advance game, Sonic Advance, as a boss. He is similar to Mecha Knuckles from Sonic the Comic. In Sonic R, to unlock him, you need to collect all 5 tokens in Reactive Factory, finish in at least third, then beat him in a one-on-one race.