After the original Metallixes formed the Brotherhood of Metallix and attempted to overthrow Dr. Robotnik, it became apparent that a design based on Sonic the Hedgehog was too unstable. Therefore Grimer developed plans for a new Metallix that would be based on Knuckles the Echidna. After Robotnik was deposed as dictator of Mobius and subsequently kidnapped by a Prosecutor of the Drakon Empire, he finally found an opportunity to put this new model into production.
Robotnik managed to convince the Drakon Emperor Ko-Dorr that Sonic was guilty of crimes against the Drakon Empire, as he had been present at the destruction of a Drakon Sentinel in the Aquatic Ruin Zone some time before. When Robotnik returned to Mobius in order to capture Sonic for the Drakons, he was accompanied by the first Knuckles Metallix, who appeared immune to all of Sonic's attacks but was able to knock Sonic out with a single blow. At Sonic's trial by combat, the Knuckles Metallix was appointed as temporary Prosecutor, at Robotnik's suggestion. Sonic got in a few early hits, knocking the Metallix to the ground with a Drakon weapon, but the Metallix then took Sonic by surprise with its death ray. Sonic managed to dodge just in time, so that he was wounded and not killed outright. After this, the Metallix proved by far the superior fighter, and would certainly have killed Sonic if not for the timely intervention of Tails, who helped Sonic escape and crushed the Metallix beneath the arena door. Despite Tails' interference, Ko-Dorr ruled that Sonic was innocent and refused a retrial. Robotnik was later seen to be developing more of these Metallixes in his base on Flickies' Island but they were never used.
Grimer was obviously proud of his creation and later used one to kidnap Sonic, squarely beating the hedgehog in a match. Fortunately for Sonic he was released with no memory of the encounter and fake rubble suggesting he had beat it, allowing his ego to remain intact.
- This character was only ever referred to as "Metallix" or "the new Metallix". The name "Knuckles Metallix" is designed to differentiate it from the Metallixes modelled on Sonic.
- The blueprints of the Knuckles Metallix appeared in Sonic the Comic #72, which was first published in March 1996. This makes the Knuckles Metallix the first robotic counterpart of Knuckles in any continuity, predating Archie's Mecha Knuckles by four months, although the Knuckles Metallix did not appear in person until Sonic the Comic #108 in July 1997. Coincidentally, the Knuckles Metallix's first actual appearance was three months before the debut of Metal Knuckles in Sonic R in October 1997.
- Sonic the Comic #108, "The Evil Empire, Part 1"
- Sonic the Comic #110, "The Evil Empire, Part 3"
- Sonic the Comic #72, "The Return of Chaotix, Part 6"
- Sonic the Comic #106, "Flickies' Island, Part 3"
- Sonic the Comic #109, "The Evil Empire, Part 2"
- Sonic the Comic #111, "The Evil Empire, Part 4"
- Sonic the Comic #116, "Best of Enemies, Part 1"
- Sonic the Comic #139, "Whatever Happened to Grimer?"