This weekend's "not a baked eel" selection is prose, not song, but it would make eminently suitable material for an original piece.
The "loathly lady" is a story type that usually goes over well today. The male protagonist is in search of the answer to the question, "What do women want?" which he must answer or else forfeit his life. After getting many answers from many people (which range from the pedestrian to the avaricious to the risque), he finds an old and ugly woman who can tell him the true answer, but only if he'll swear to marry her. He does, and she reveals the answer: Sovereignty. Later, she offers him a choice that can magically change her appearance - but he lets her make up her own mind on the matter, which is how her curse is undone.
The most famous of these stories is surely The Wife of Bath's Tale. In this one, the lady is old and ugly, and she tells her new, reluctant husband that he can have her fair and faithless, or foul and faithful. I first encountered the trope in The Wedding of Sir Gawain and Dame Ragnell, in which Sir Gawain, also faced with a loathly bride, has the slightly different options of fair by day and foul by night (which would win him renown in court, for having a lovely wife) or the reverse (which would make him a happier man). John Gower's Tale of Florent is yet another version, which I admit I haven't heard of before today.