人狼之恋 Nazareno Cruz y el lobo (1975)

Nazareno Cruz is the seventh son of a couple living in a high mountain village. According to a myth, a seventh son will become a wolf on nights of the full moon. Everyone in the village is relieved when this doesn't happen. The boy grows up and falls in love with a beautiful girl, Griselda. When he's 20 years old, he is visited by the Devil, who offers him the wealth of the world if he will turn his back on his love for Griselda, and if he fails to do this, he will become a wolf.