The House by the Cemetery (1981)

A New Yorker, Norman moves his wife and son, Bob into a creepy, run down New England mansion in order to continue his research into the 19th century surgeon Dr Freudstein who's experiments led to him losing his medical license and being banned from the medical profession for life.

Dr Freudstein in his later years.

...And now would be a good time to mention that the creepy run down New England mansion the family moves into is the former home of Doctor Freudstein. And that Norman is actually continuing the research of a colleague of his Dr. Peterson who committed suicide while researching Dr Freudstein experiments. And that there is a history of deaths and disappearances in this house. And that Bob has an "imaginary" friend who tells him to leave the house. And that the basement door is strangely sealed shut. And that Dr. Boyle discovers that Dr Freudstein was never actually buried in the cemetery records say he was...  needless to say, if you're familiar at all with the horror genre you should be able to pretty much piece the whole movie together from that. Still this is a really fun and creepy movie.

Bob will save his family from the evil thing in the basement.

This is movie number three in legendary Italian horror director, Lucio Fulci's unofficial Gates of Hell trilogy. Consisting of this movie as well as The City of the Living Dead (1980) and The Beyond (1980). They're not a trilogy in the sense that they share a common continuity, but they are a trilogy in the thematic sense, each of them revolve around a gateway to Hell (these aren't figurative gateways either). And all three of them are super creepy.

If you call yourself a horror fan at all, this one is a must see (as well as much of the rest of Fulci's work, but that's probably a subject for another article).

The House by the Cemetery (Imdb)