Please don't list this on a work's page as a trope. Examples can go on the work's YMMV tab.
Nightmare Fuel: For a Few Dollars More
El Indio was frightening as hell, and a villain quite unusual in Sergio Leone films. Worse, in all Sergio Leone films, he's the only villain that's completely incapable of being reasoned with. The following villains, Angel Eyes and Frank are downright sadistic sociopaths, but still can reason with them. That won't work with El Indio. He's just a mentally unstable man who just likes to kill —including his own minions—, period. This is evident in the flashback, he is capable of the most atrocious things for no reason.
The simple fact of his insane laugh in his wanted poster is enough to scare or disturb someone.
The scene where Mortimer and Manco are tortured is somewhat disturbing, especially because this is just For the Evulz.
The flashback, especially considering it has some elements of a Thriller film: it's a one dark night and raining, El Indio enters in a house and proceeds to kill the boyfriend of the Mortimer's sister, and proceeds to rape her up to the point who committed suicide. The music in the flashback also counts.