Walking Dead has some sad ones. Since a lot of folks already mentioned some good ones.
Spoilers for Walking Dead.
Noah, being ripped apart in the revolving doors, it also mirrors the deaths in Day of the Dead (OG) spectacularly.
and of course
Glenn, though it hurt, I'm glad they stuck with the comic route for his character because it is such a linch pin moment for the group.
Hereditary, pretty much any of them barring
The son, which was kind of goofy IMO, but the mom severing her own head off with a piano wire was intense AF
Getting into some darker territory, there are two particular kills in a set of gruesome and unsettling kills in a movie known as When Evil Lurks, an interesting take on demon possession film.
Little girl gets rag dolled by a big dog, and a boy is being ripped apart by his own mother in one scene, it's truly awful.
"There will be nothing to show that we were ever here... but stardust." - Pinbacker