This transformation exists primarily or exclusively within the Pre-Super Genesis Wave continuity. Information in this article may not be canonical to the storyline of the games or any other Sonic continuity.
Having become Chaos Knuckles before, Knuckles attained this form once more when Dr. Eggman intruded on Angel Island, and used his powers to defeat Eggman. Unfortunately, Knuckles became corrupted by this form's sheer power, and set out to rewrite Light Mobius as he saw fit. In the unaltered timeline, he succeeded in restoring his girlfriend Julie-Su to a fully organic state before being confronted by Sonic. Using an alien device known as the Nullifier, Sonic was able to return Knuckles to normal-though at the cost of the Echidna's right eye.
Writer Ian Flynn has stated his opinion that in the altered timeline of Light Mobius, Chaos Knuckles played much the same role, but was instead stopped by King Shadow.