Carreg y Bwci 1
Image by Kammer
Carreg y Bwci

Rhiannon​…

And, presumably, Shakespeare's 'Puck' in a Midsummer Night's Dream...
J
x

don't forget the Welsh bwca and bwbach, or the north's boggles and boggarts

all descendants of Bu

Puck, yes, but in English folklore (where he's the will-o-the-wisp) more than in Shakespeare.