This is based on opinion. Please don't list it on a work's trope example list.
Nightmare Fuel / The Howling
Pretty much all of them feature this in some way (though the third one is perhaps the most divisive). New Moon Rising features a lot of horrifying stuff as well... just not the stuff that the director actually intended to be horrific.
"I'm gonna give you a piece of my mind." Right before Eddie's transformation, he pulls part of his brain out through a bullet hole in his head.
Everything about Eddie Quist qualifies as nightmare fuel
The werewolves themselves (in the films without Special Effects Failure, namely the first one) are most certainly not pretty sights. The fact they are often evil people who still have control over themselves leads to a lot of It Can Think moments. Eddie Quist isn't a mindless predator, he's a super powered serial killer.