"Indeed (IMHO) 'The Twa Magicians' was written by Peter Buchan in the early 19thc "
Is there any actual evidence of this Steve?
It seems to me that shape-shifting has been a part of folklore as far back as Homer and has surfaced constantly in folk literature.
Attributing is to someone you have made a poing of not approving of without evidence to back it up is somewhat iffy, to say the least.
Jim Carroll