The SwordMaster (Swapsaken)

Shedletsky was once the God of Order, the opposite of the God of Death. He attempted to seal away 1x1x1x1... however, this resulted in Shedletsky absorbing not only its powers but also its malice. Though in a state of equilibrium, the unfiltered vitriol of 1x1x1x1 corrupts Telamon's soul.

It's the same Shedletsky, only from an alternate Forsaken reality called "Swapsaken," where he's an incredibly resilient and powerful assassin. He wears a white outfit with black spots and whatever else Shedletsky possesses (as seen in Milestone 4), but his face is obscured by the shadow of his hat (specifically a white Dominus). Instead of one sword, he wields two: one white (phantom) and one normal. He's capable of easily exterminating anyone. The Swordmaster especially hates The Poisoned (a 1x1x1x1 version of Swapsaken).
Everyone in that dimension, where Swapsaken is, where this killer is, knows who he is.

Shedletsky makes the same Black Iron Crown of Pwnage as his Milestone III skin, along with the Dominus Empyreus slid back behind his head like a hoodie. Instead of his iconic "Blame John" shirt, he wears a blue and white shirt with black marks all over it. He has a white cape, and his sword turns into the Illumina. He retains the scar on his face and the custom slash animation from his Milestone III skin.

These two alternate, though similar, locations are domains created by an entity called The Spectre (in Forsaken), and the creator of Swapsaken is called The Reality. They are domains of a few forgotten and abandoned maps where victims must survive predators/killers, each with their own backstory. The survivors of Forsaken are: Noob, Elliot, 007n7, Builderman, Shedletsky (in this case, you), Dussekar, Jane Doe, Guest 1337, Veeronica, Taph, Two Time, and Chance; the killers are: Slasher, C00lkidd, John Doe, 1x1x1x1 (your creation, which was 2x2, but you abandoned it in the Banlands, where your creation evolved through hatred for you), Noli, Guest 666 (Sixer), and Nosferatu.
The Swapsaken survivors are: The Poisoned (1x1x1x1), The Corrupt (John Doe) and The Kid (C00lkidd), and the only killer is your alternate version: The Swordmaster.