Mecha Knuckles is a robotic version of Knuckles the Echidna created by Dr. Eggman. He appeared in Sonic Advance as the boss of the Angel Island Zone.
Mecha Knuckles appeared at the end of Angel Island Act 2 and was covered in an artificial epidermis to make him appear as the real Knuckles (though its epidermis was magenta whereas Knuckles' fur is red). It attacked Sonic the Hedgehog using the same abilities as the real Knuckles until Sonic destroyed its outer covering, revealing the metallic endoskeleton beneath. The robot then attacked by launching abnormally large missiles from its chest. After suffering another four hits, Mecha Knuckles was destroyed and Dr. Eggman, who had been observing the battle, fled.
Mecha Knuckles attacks by spin-dashing, jumping and gliding. He will punch the player if they attempt to dash into him. After losing his false skin, he starts launching comically-sized missiles from his chest as well as using glide attacks.