Black Christmas (1974), directed by Bob Clark.
Aka Silent Night, Evil Night. Made in Canada but set in the US.
I wanted to see this because (1) it stars Olivia Hussey, and (2) it has a following as the prototype slasher/dead teenager/sorority house of death story.
Quite a lot of comedy. In particular, the drunken house mother is a hoot.
The dementia of the psycho killer approaches the demonic, but we never get an explanation. A little of this goes a long way with me.
The Blu-ray picture looks like an average DVD.