- Magneto. He's even more ruthless and vicious than his mainstream counterpart with a Fantastic Racism towards humans (and pretty much anything else not mutant) that surpasses anything the typical Magneto would indulge in. He's so bigoted towards humans he planned to have them used as food stuffs and cattle for his mutant forces after he completed his plans for domination. He's responsible for habitual terrorist bombings that kicked off the abominable prejudice towards mutants in the verse, millions of deaths, and massive protagonist death considering he kicked off the Ultimatum arc by stealing Thor's hammer to offset the Earth's magnetic poles, making him the verse's most infamous and widespread Hero Killer.
- Some members of the Brotherhood also qualify as terrifying themselves, notably Mastermind and Pyro who were shown trying to gang rape Valkyrie after incapacitating her and the disgustingly obese mass of flesh The Blob, a confirmed cannibal who threatens to eat his enemies in battle and was outright shown to have eaten the Wasp during the Ultimatum event.
- The cheapness of mutant life is even more blatantly horrific in this continuity with Sentinels being sent into populated streets to find and kill unsuspecting mutants. Just being born one is tantamount to a death sentence. There are even reality shows such as the version hosted by the Ultimate Version of Mojo where mutants are hunted like animals for the entertainment of bigoted and sadistic masses. Made even worse Post-Ultimatum, where a government executive order has decreed all mutants are to be apprehended to be sent and crammed into internment camps or executed on sight because of Magneto's misdeeds. Even if allowed to live and appear as baseline humans, mutants have to suppress their powers even during bullying and attacks or they'll be rounded up and put in camps.
- Weapon X and their treatment of mutants is non-stop nightmare fuel in-verse. They're a division of S.H.I.E.L.D. run by a particularly nasty Sociopathic Soldier among a garrison of the same that's been going around kidnapping, torturing, brainwashing, and training mutants, notably teenagers, to be living killing machines for their agendas. They treat their mutant captives like abused animals, ritually torturing them for fun and forcing obedience through repeated mind wipes and sub-cranial explosive implants they promise to detonate if the mutants misbehave during possible suicide missions. They're first shown beating on an escaped Nightcrawler, mocking him and beating him for the escape attempt, and promising to increase the tortures to show the mutants they are in change. They're such a Knight of Cerebus that they even force Jean Grey of all people to commit murder under threat of ending Cyclops' life, gruesomely experiment on Beast to give him his blue animal form, and actually convince much of the X-Men to try and break their Thou Shalt Not Kill rule. Humans Are Bastards Indeed!
Colonel Wraith: Close down Weapon X and who's going to save the world next time some lunatic with the wrong set of genes decides to play football with the President's head? Are you going to ask Spider-Man for help the next time the mutants attack the White House?
- Even more unsettling is that the group was created out of the fear of the growing mutant presence that was happening around the world and the evident growing threat of genocidal mutants like Magneto running rough-shot over the United States such as when he took over Washington DC and made the US President lick his boots clean while naked on national television. The fact there was no reliable superhuman defense force besides the capricious and privately held Ultimates at the time really clinches the horrible notion that as evil as Weapon X is, they may have actually been necessary to save the world from worse threats. Actually lampshaded by Colonel Wraith himself when his superior tried to have Weapon X decommissioned.
- Wolverine's entire backstory is even more nightmarish than in the mainstream. He was a soldier captured during WWII because of his ability to heal from damage that killed his compatriots and was experimented on to be used as the progenitor of the mutant race. After which, he spent his many years of his life as a Weapon X lab rat and trained killing machine while being personally tortured in a variety of awful ways (i.e. being riddled with bullets, set on fire, skull cracked open, blown up, electrocuted, etc.) by his prison guards all For the Lulz before having his mind wiped and sent on missions only to be dragged back to experience the torture all over again. Note this part was after the adamantium was grafted to his bones, giving a glimpse of what things would be like for Wolverine if he had the sort of life his clone X-23 had to experience by not escaping soon enough.
- One short story in Ultimate X-Men #41 involves a kid (as seen in the page image) who wakes up one day, and finds his family is gone. He goes out onto the street, and everyone else is gone. He spots some people, looks away, and then they're gone when he looks back. And there's empty clothes lying around everywhere... When Wolverine tracks him down hiding in a cave nearby, he calmly explains to the kid that he's a mutant, and his power is the constant excretion from his skin of an array of chemicals that dissolves flesh and bone. And he can't shut it off. Ever. So, for the sake of all humanity, he's got to put the kid down. The kid agrees with this, and submits calmly to his execution at Wolverine's claws.
- Proteus, the body-hopping reality warping psychotic son of Charles Xavier with years of And I Must Scream treatments and Daddy Issues under his belt. His first appearance has him hopping from person to person, killing them by wearing out their bodies, before being cornered by the X-Men. He then kills a whole restaurant full of people in an instant before hopping into Wolverine and makes him get run over by a truck before escaping, with the sight being so gruesome it terrifies all its spectators, especially Proteus' mother who described Wolverine healing himself afterwards as an "autopsy in reverse". Proteus then hops into Betsy Braddock, Britain's most potent telepath, and hides in plain sight to screw with his father before deciding to start ripping up reality and morphing Betsy's body to match his own, starting with his head on her exposed feminine body. To add to the horror, he's also telepathic, meaning he can easily read your mind and find out your deepest fears to deliver the right Hannibal Lecture needed to break your spirits in addition to conjuring up some nasty supplemental images with his reality warping powers. Like the mainstream continuity, he's one of the only characters this continuity's version Wolverine of all people is truly afraid of.
- Jean Grey's Character Development Post-Ultimatum is pretty unsettling with inspection. She went from an idealistic hero and The Heart of the X-Men who strongly advocated a Thou Shalt Not Kill stance to a murderous dictator planning assassinations and murder attempts on her own former teammates. All because she went through one too many Break the Cutie moments.
Nightmare Fuel / Ultimate X-Men
If you thought the nightmare fuel of the mainstream X-Men was bad, the horror show that mutants are trapped in within the Ultimate Verse will kick things Up to Eleven. Some horrific examples of nightmare fuel found in the dismal world of the Ultimate X-Men include: