Could be remade as a pretty good horror film today

Yeah, it suffers from the standard problems of low-budget movies of the day, but the story itself is really pretty horrific, especially Pantoja's death - the Baron hypnotizes the guy so he can't move, then seduces his wife in front of him, then morphs to the demon, kills her by sucking her brains out, and finally kills Pantoja.

A modern R-Rated treatment of that scene alone could be really chilling.

--
Philo's Law: To learn from your mistakes, you have to realize you're making mistakes.