This is an extremely vague memory I have of this movie. I can say it was from the late 1970's to the very early 1990's. It was a fantasy movie.
The only scene I remember clearly, or at all, is near the beginning, there is a really cool effect where there is either a demon or god in the sky that is made completely of clouds. It looked like they created it completely from stock footage of clouds and just placed them over each other to give them a shape.
That is really all I can recall. I am aware this is a long shot.
For some reason I always had it in my head that the movie was Cronos, I was incorrect.