This is based on opinion. Please don't list it on a work's trope example list.
Nightmare Fuel / The Mummy Trilogy
In the backstory of the first film, Imhotep is sentenced to endure a horrible curse known as Hom-Dai, which grants eternal life, which involves cutting his tongue off. He is then devoured by scarabs so that he'll eternally have to endure the agony of his wounds. His fellow priests don't fare off that much better, they are mummified alive!
Worse in the novelisation, which has the latitude to go into deeper detail about the curse without pacing or rating issues. It seems that the curse was designed to work in a twisted mockery of the "circle of life"- Imhotep is eaten by the scarabs, and eventually becomes so ravenous that he begins eating them, they eat him all over again...
In a meta example, after filming this scene, being tied up not being Arnold Vosloo's favorite thing, due to the claustrophobia of being wrapped and entombed in the sarcophagus.
The scene at the prison when Rick almost strangles to death at the end of the hangman's noose is... somewhat unsettling. Unpleasant enough that it's cut from a lot of television showings, put it that way.
Even worse when you consider that Brendan Fraser himself almost died filming that scene.
The scene where the diggers open the tomb with the Book of the Dead and salt acid sprays out of the opening and douses them in it. They are in complete agony, and Rick mentions they "melted".
The blue gold scarab. The real thing breaks out of the pretty shell and kills a man by tunneling through his flesh... and eating his brain.
The scenes where Imhotep re-makes himself out of bits of living people...
The scarab crawling out of Imhotep's neck, back through the hole in his cheek, and he bites down with a crunch.
Beni's eventual fate. Trapped in a dungeon that's just been permanently sealed under the desert, only a single torch to keep you safe from the flesh-eating Scarabs which are gathering around you, and you have to sit there and watch while they surround you and you watch the torch slowly... flicker... out.
As far as Jerry Goldsmith's score for the film goes, probably the most chilling and disturbing track is "The Crypt". Do yourself a favor and don't listen to it when you're alone at night.
The pygmies. Oh good lord, the pygmies.
In the second film, there's a moment where Ahm Shere is returned to its former glory. It is done so by a museum curator wearing the bracelet putting his arm into a hole in a stone statue. I don't think I want to know what that crunching noise was and why he was screaming in pain...
But then we get to see his hand which is nothing more than a skeleton with some gooey substance that looks like saliva clinging to it. Which begs the question: What ate his hand?!
In the third film, the Taken for Granite aspect of the Terracotta Warriors. It's not so much the fact that they are this since you see that in many a movie (though it's still quite unsettling), but the process. Just... watching them as they start to liquify from the mouth, the wet clay leaking out as it spreads and takes over their forms, hollowing their bodies out, covering them... Brrr!
The second movie starts off with an archeological dig. One hole is dug up into a swarm of scarabs, which begin attacking people. One guy manages to make it out, only to see bulges moving around under his skin before the bugs come out of his mouth.
This troper is actually quite unnerved by Arnold Vosloo's performance in the first film. He's truly terrifying as Imhotep, and not someone you'd want to run across in a dark alley (Imhotep, not Vosloo, who seems to be a pleasant fellow). Shame he pretty much becomes a background character in the second film.