This is by far the scariest piece I've ever heard. What are yours?

Der Leiermann for me is the scariest song of the many I've listened to. I sung it in a recital last summer and it froze the audience. Truly terrifying (the audience spoke german mostly so it was quite helpful for the mood.) Sadly this isn't me singing btw incase you don't know lol.

Xenakis, Penderecki, Ligeti...

I'm going to commit heresy and say that, for me, it's the score to the Red Wedding....

Such big chords only to become so sparse right after. Other pieces of Classical Music that are often considered scary like say Toccata and Fugue in D minor, I don't consider them scary at all. But Don Giovanni, certainly a scary piece written by a composer that often writes happy music.

Interesting topic! For me it would probably be Saint-Saëns’ Danse Macabre. I find it haunting, especially with the dissonant violins.

I think this music is also used in the movie "The Shining" (I am referring here to only the 1st movement of the multi-movement work)