Thanks Null for the Photos

MX is a horrorbrew owned by @RazzDazzleDoo. He is the main antagonist in the Creepypasta game Mario '85, which is meant to be a love letter to the original Super Mario Bros. game.

He's an unknown entity who inhabited a copy of Super Mario Bros. and disguised himself as a slightly-off version of Mario in order to lure unsuspecting players/victims into the game and play with for all eternity. He is Lucas's tormentor, of whom he killed and pulled his soul into his digital hellish dimension, forcing him into the body of Luigi.

More facts here: https://house-of-horrorbrews.fandom.com/wiki/MX