the only thing i remember about this movie is that is was made in the 90's. It was about a boy and his father. The father was about to marry this woman. The woman turns out to be a monster or something like that. The boy finds out and tries to convince his father not to marry her. I remember one seen where the boy walks in to the womans room and sees her tail. And then he runs away.
The movie mentioned above was about a father and daughter.
Dan Akroyd from S.N.L. played the father and Allyson Hannigan from Buffy played the daughter.
Also Seth Green had a small role in it too.