A social misfit, Willard is made fun of by his co-workers, and squeezed out of the company started by his deceased father by his boss. His only friends are a couple of rats he raised at home, Ben and Socrates. However, when one of them is killed at work, he goes on a rampage using his rats to attack those who have been tormenting him.

https://www.themoviedb.org/movie/42532-willard

The movie follows a Los Angeles bookstore worker who becomes engrossed in a horror novel titled I, Madman, and finds a series of murders resembling those in the book occurring around her.

https://www.themoviedb.org/movie/40353-i-madman

Sometimes called "The Soviet Union’s first horror film", Viy is a movie about a seminary student having to survive three nights alone at the wake of a witch in a remote village.

https://www.themoviedb.org/movie/57230

The other posters for this movie range from bad to terrible, but this one really stood out to me.