Jaspers is kind of part of that trope of omega mutants who can reshape reality like Franklin, Jamie Braddock, Proteus or Legion.
In the original Alan Moore story he was killed by the Fury, his own creation, by being ported outside all realities and killed there, where there was no reality to manipulate.
He was a Omniversal threat for a while, after his death at the hand of The Fury he went to oblivion, but was resurrected along with a shard of the Fury inside thanks to House of M, and proceeded to wreck the Exiles, excalibur and the entire omniversal Britain corps, just to be taken over by the Fury and become it himself.
Most of that fight i have found there
That happened in Exiles and Uncanny x men in the "Die by the Sword" crossover.
There was an alternate jaspers in a x men 4 issue in Astonishing x men called Xenogenesis, but both him and the fury in this story appeared quite depowered and there was an army of Furies that worked like omniversal travelling sentinels basically.
the Fury showed up again but no jasper this time in a Uncanny X men story written by Claremont, it was Jamie Braddock that made it attack and almost wipe out the x men in a fell swoop (they had to use phoenix powers and amplified mutant powers combined to throw it in a pocket universe basically) to unite them in view of a future cosmic threat (some kind of Anti-phoenix).
His Fury acted like a true powerhouse, one punching rachel phoenix in orbit and breaking the invulnerability of cannonball
To defeat it, they had to go "planeteer" on its cybiote ass to bfr him in a pocket reality prison basically...
and in a two parter on Marvel Heroes 15-16 in a what if kind of world it kind of killed the entire Marvel universe until Galactus gave the heroes a ultimate nullifier...
It showed up again in Secret Avengers, but mostly as a joke character, A fury that can be beaten by two human characters by simply jettisoning it to space. Granted, it was a pregnant with extradimensional chtulus babies Fury, who had familial feelings apparently.
Don t ask, no one wants the mental image. Yet, here it is anyway implied.
Right now he should be dead, and the last Fury seen was fused to the human Fury in the ultron army in Secret Wars Siege, Kang managed to beat it by riding it through a barricade of chronomines at the expense of his own life...
In the end Jaspers can be as dangerous as any deranged universe-altering reality manipulator, at the current time i can see him play out as on par with a Cube being.