- Every scene with the lobotomized Jason Stryker. Regardless of whether or not he's truly as malevolent as his father claims, he's just creepy.
- Speaking of which, the backstory William Stryker gives is absolutely horrific. If Jason really did do what his father claims he did, then he is easily one of the most terrifying villains in not only the series, but the entire superhero genre. To elaborate: Jason tortured his own parents by projecting horrific imagery into their minds. We are not given details, but apparently they were so bad that Jason's mother lobotomised herself with a power drill rather than endure them anymore.
- Mitchell Laurio, the warden who bullied Magneto in his plastic prison, gets a pretty gruesome (although not undeserved) death, with the iron Mystique injected in his body for Magneto to use to break out bursting out of his chest capillaries when Magneto attracts said iron.
- When Stryker's men silently invade the X Mansion, quickly sedating and abducting many children. Furthermore, their face paint is quite unsettling.
- The grey eyes that characters get when under the influence of Stryker's mind control serum.
- When Xavier inadvertently uses the Dark Cerebro to slowly eliminate all mutants or all humans, they are shown unable to do anything except writhe in pain and agony. What of all the surgeons, pilots, etc?
- The notion that Xavier is fully capable of killing anyone on the planet by using Cerebro to focus on a target to induce brain death is terrifying in itself. The fact Magneto of all people tried to make Charles do this to all of humanity after literally just stopping Stryker from doing so to mutants is even more repugnant.
- While it was an immense and exciting visual spectacle, the opening, featuring Nightcrawler taking down every one of the president's bodyguards is also quite unsettling. The ease at which he quickly and efficiently dispatches each and every one of them... And the fact that he was a second away from stabbing the president; had that last bodyguard not recovered at the last minute to graze Kurt's shoulder with a bullet, things would've been much worse for the mutant population.
- The blurry disorienting flashbacks Wolverine experiences throughout the film. The last one is him escaping the Weapon X facility where he staggers down a dark tunnel and looks at his claws with a horrified expression and loud scream, covered in blood before the memory abruptly ends.
Nightmare Fuel / X2: X-Men United