Not sure it is my favourite, but I was haunted by THE SECRET OF ROAN INISH, from 1994.
The move explores a legend about a selkie, a creature that is part woman, part seal. And if a man can steal the selkie's skin, which she sheds when she comes to shore and takes on the shape of a woman, he can marry her.
That sounds fabulous. I'd be sure to enjoy it. I actually mentioned a selkie in passing somewhere in Mistress. She's a kind of Irish bunyip. You have more information than I had though ... more than I needed.