Sonic Channel featured a Japanese profile of Metal Knuckles. Translated, it states,
"As with Sonic, Eggman prepared this secret weapon for the sake of overthrowing Knuckles, considering his existence to be a hindrance. Having the same power plant as Metal Sonic, speed and acceleration power are high, but like Knuckles, this robot can glide from high places."
Appearance requirements: Collect 5 tokens in Reactive Factory in Grand Prix mode and finish better than fourth place to begin a one-on-one match with Metal Knuckles. Win this race and Metal Knuckles will become a possible choice on the character select screen.
Metal Knuckles is just like Knuckles The Echidna but with green eyes.