This creature was summoned from a dark and uncharted dimension by the Three Witches of Itchstump Island. They were seeking vengeance on Duke Gurth the Odious for a poorly worded Christmas card, which started a cursed fire that killed nineteen people and a particularly favored newt. While the Witches originally intended to simply summon an imp capable of carrying an insulting musical greeting card, their anger increased as they reminisced about all the injustices and petty cruelties visited upon them by Gurth and the other Dukes. Eventually the witches just started trying to summon the biggest monster they could find, and to hell with the consequences. They had their heart set on a creature the size of Mount Krullmore, three miles tall, with spikes the size of battering rams and lava breath with a range of twelve miles; but the Green Monster showed up first and ate the nearest witch to the dimensional portal, closing the portal and making the point moot.
The Monster is not of this world and does things for reasons that seem completely random at times. Only the Dukes are capable of commanding its respect, and even then only when they're looking directly at it. When not actively destroying things, places, and people for one of the Dukes, the Monster is actively destroying things, places, and people for its own weird reasons. It’s been known to beatbox while engaged in its peculiar brand of tentacular slaughter. It gives off a distinct odor of nutmeg and flatulence.