WARNING: The following contains spoilers for X of Swords: Creation by Jonathan Hickman, Tini Howard, Pepe Larraz, Marte Gracia and VC's Clayton Cowles, on sale now.
Marvel's new X-Men crossover, X of Swords, has pitted the X-Men against the First Horsemen of Apocalypse, who happen to be Apocalypse's own children. This has quickly turned into an all-hands-on-deck event for the X-Men and their various mutant allies.
While X of Swords: Creation #1 called in characters from the far reaches of the X-Men's world, it also revealed the current locations of the most dangerous foes teh X-Men or any of the team's members have ever faced. As a text piece in the issue revealed, two existential threats to the X-Men and Captain Britain, Mad Jim Jaspers and the Fury, are in control of over their own courts of Otherworld. Even though they're isolated in their own worlds for the moment, the fact that they even still exist somewhere in the Marvel Multiverse is cause for alarm.
Mad Jim Jaspers was created by Dave Thorpe and Alan Davis. First appearing in Marvel Super-Heroes #377. Mad Jim Jaspers was a member of the British Parliament on Earth-238, where he managed to convince his world to outlaw superheroes. Unbeknownst to anyone, Jaspers was secretly an Omega-Level mutant, with the power to warp reality with his mind, at the cost of his sanity with each use.
Seeking to be the only superpowered being on his world, Mad Jim created the Fury, a "cybiote" a kind of cyborg designed to hunt down and kill any intended target. Building this creature with adaptational abilities and an advanced healing factor, Mad Jim let it loose upon his world. In the span of a few years, the Fury managed to kill every superpowered being on Earth, save for Mad Jim, whom it wanted to kill, but could not due to its programming.
With no one to stand in his way, Mad Jim prepared to unleash the Jaspers' Warp, which would have unleashed a wave of unreality across everything in the multiverse. Fortunately for the multiverse, Saturnyne was trying to give his reality "The Push," an evolutionary leap forward but stumbled upon his plans instead. Fearing what could happen if Jaspers was allowed to go through with his insane plan, Saturnyne's temporary replacement, Mandragon, destroyed the reality of Earth-238, killing Mad Jim and sparing the multiverse his insanity.
But while Jack may have died, his last creation did not go into the void willingly. Not at first at least. Having encountered the Captain Britain of Earth-616, the Fury had no choice but to follow its programming and pursue the hero. But while it was there it encountered the Earth-616 version of Jaspers. Not bound by its programming there, it attacked him. The struggle was violent, but with its adaptation abilities, the Fury dragged this version of Mad Jim to its home dimension, which by then had been destroyed by Mandragon. With no reality to manipulate, Mad Jim was quickly lobotomized by the Fury.
Satisfied with the results of its work, the Fury returned to Earth-616, only to be attacked by Captain Britain. It was beaten so badly that it could not recover from its injuries. And that appeared to be the end of that madcap story. But if the notes section of X of Swords: Creation #1 is to be believed, then not only do the Fury and Mad Jim Jaspers still exist, but they are each in control of their own kingdoms.
While these could be other versions of the characters from elsewhere in the multiverse, the very threat of either of these powerhouse villains is an existential threat to what the X-Men have built on Krakoa and the Marvel Universe as a whole. And even though the X-Men might be busy getting ready to deal with the First Horsemen and thier armies right now, either one of these villains marks a major new potential threat on the horizon.