Tom
"a ballad of magical activities;"
There's no great evidence for this; the conclusion that it is a supernatural ballad seems to be based on the title 'Elphin' or 'Elfin Knight'
The Standard Dictionary of Folklore makes the point '...the elfin-ness of the knight plays no essential part in the story'.
Child gives a number of parallel folk tales all based on trickery and cleverness on the part of the woman, rather than magic.
I think there is a danger of over-complicating these ballads by reading aspects into them that are simply not there.
The most blatant example of this is to be found in Phillips Barry's note to 'The Lake of Col Fin' in the New Green Mountain Songster, manages to turn what is one of our most beautiful songs concerning domestic tragedy into a tale of enchantment, magic islands and water nymphs.
Jim Carroll