- Sebastian Shaw's inexplicable afterimages after absorbing energy, especially that of a nuclear reactor in the climax. You're seeing what a Voice of the Legion would look like.
- Azazel, Shaw's teleporting mutant, took people from within the CIA base and appeared in the sky before dropping them to the hard ground below! Now, think of going to sleep only to wake up in the air and FALLING.
- The mere fact that a quite high amount of both humans and mutants are fine with genocide.
- Charles reading Emma's mind, seeing Shaw's plan of causing a nuclear apocalypse through which only mutants would survive, culminating in Hellfire Club taking over what's left through a dictatorship, with the image of them standing over the smoking ruins of Washington DC and the White House, with crowds shouting "President Shaw". Then Emma gives us this gem with a smile:Emma: Beautiful, isn't it?
- Charles reading Emma's mind, seeing Shaw's plan of causing a nuclear apocalypse through which only mutants would survive, culminating in Hellfire Club taking over what's left through a dictatorship, with the image of them standing over the smoking ruins of Washington DC and the White House, with crowds shouting "President Shaw". Then Emma gives us this gem with a smile:
- Charles screaming in pain as Erik is slowly and deliberately drilling a coin through Shaw's head, who Charles was telepathically connected to at the time. The thing by itself is horrific, and this makes it even worse (it's essentially experiencing death without actually dying).
- Hank's transformation into Beast. His physical body goes through five notable changes from jaw line to claw growth. Then there's being blue and fuzzy for the rest of your life... All of that from trying to get rid of hand-like feet.
- The Hope Spot ensuing from Hank injecting himself with the cure. We all suspect something can go horribly wrong, but we see his feet change back to a human. Seeing this, Hank is amazed, believing he has found a cure. But then his feet change back to its mutant form, and start to grow blue fur. And that's when the audience can worry...
- Darwin's extremely horrifying death, slowly being burned from the inside out. The audience can see his body trying to fight it. The worst part is the end; he reaches out to Alex, face completely calm, and disintegrates.
- The scene where Erik Lehnsherr, while interrogating a bank manager, pulls one of the metal fillings in his teeth out with his powers. Mercifully less graphic than it could have been, but still cringeworthy.
- The look of pure volcanic rage that crosses Erik's face when Charles tries to talk him down from massacring the Soviet and US sailors, insisting "They're just following orders". Adding to this is the look of horror on Charles's face when he realises he's said the worst thing imaginable, as well as the tone of fury Erik replies in.
- According to a deleted scene, the whole reason why Alex was even in solitary in the first place was because he'd had a "violent altercation" with two men in the prison showers. Now, keep in mind that by this point, Alex is only all of seventeen-nineteen years old. What other reason would those men have had for confronting him?
Nightmare Fuel / X-Men: First Class