Parallelisms

Anyone who reads mythology knows that certain elements are always changed to suit the place of origin while there are still commonalities among the myths in question. The following conversation just took place between mom and me while discussing the possible subject of the Spring KAL on Ravlery's Folklore&Fairytale group:
Me: It was a goat.
Mom: A goat?
Me: It wasn't a sheep. It was a goat.
Mom: A goat that did what?
Me: That he was standing on.
Mom: He was standing on a goat to get into his bathtub?
Me: Mmmhmm.
Mom: Peculiar man. That's no reason for him to be lanced or whatever. And I thought your father was peculiar...
Me: (busy giggling)

This came up because one of the stories proposed as a candidate for the KAL is that of Blodeuwedd; a version of it appears in the Enchanted World Series book Wizards and Witches, which is the only one I've read. The short version is that Lleu's teacher Math, son of Mathonwy, creates a companion for him by making a woman out of flowers. Pretty, smells nices, but not very bright, poor child, and ultimately the epitome of the faithless woman... more on that later, or you can refer to the above conversation and draw your own conclusions. Stop reading now if you don't want major mythological spoilers. :P
Blodeuwedd suffers a bit of boredom and takes a lover who, surprise, takes it in mind to get rid of Lleu. Lleu, lucky boy, is one of those people whose death can only be caused if the conditions are just right, and of course he's not likely to impart that information to just anyone. And that's where I'll stop, though I'll add that, presumably (and since I neither read nor speak Welsh, I can't verify this) the Welsh name for a barn owl will look remarkably familiar.
Now, this is where the parallelism bit comes in. A number of stories, usually revolving around a woman who's the captive of a giant or a dragon, make use of the notion that the villain's demise can only come about if certain conditions are met. The woman usually manages to wheedle the information out of her captor and said information occasionally indicates that the monster's only vulnerable place--in many cases, its heart--is stashed somewhere difficult to reach: In such-and-such place, the hero finds a boar, and inside the boar he finds a hare, and inside the hare he finds a this, that, or the other, and after all the layers are removed, behold, we have the beast's heart.
I'm not sure what conclusion to draw from all this, or how it all relates to Lleu, Math, and Bloddeuwedd, other than there are threads going all over the place, and that some of them are almost parallel (geometrically impossible, I know, since lines are either parallel or they're not). And never stand on a goat to get into your bathtub.