The Man and the Monster (1959)
This 1950s Mexican import is different from many of its contemporaries because it doesn't play to the lowest common denominator. It isn't sleazy, exploitative, or silly. It's actually quite an intelligent rethinking of the Jekyll and Hyde mythos, though admittedly with a little cheese thrown in.
A pianist wants to become the world's greatest, so he sells his soul to Satan. In a trance and under the Devil's power, he kills off the one woman who stands in his way. However, the former competition left behind an odd piece of music, one that, when played, transforms the usually meek pianist into a monster, one who raves about being the greatest, and who, of course, likes to kill. So, the pianist should just avoid playing the piece, right? Could Dr. Jekyll avoid becoming Hyde? The problem is, our pianist is compelled to play this damning bit of music every time he sits down in front the ivories. There are some other bits of weirdness involving the man/monster, but it wouldn't be fair to tell... you have to find this movie on your own.
Intelligently dubbed (it looks like they hired a translator AND a screenwriter), marvelously acted, and nicely directed, there's not a lot The Man and the Monster isn't, except, perhaps, expensive. Yes, unfortunately, the low budget shows in every scene involving the bestial side of the pianist, because the makeup is sub-par, especially the apparently foam rubber nose. However, a beautiful villa, with a lush interior, makes up for some of this, and really, it's a tiny nit to pick. All in all, a fine film.