Difficult to say.
Jiri Barta's 1986
Krysar comes to mind. It's a very weird Czech adaptation of
The Pied Piper of Hamelin, complete with a wild European prog soundtrack. It's possible that I like the 1967 folk horror film
Viy better, but
Krysar is really more unsettling.
Below:
https://vimeo.com/192649758