Dinnshenchas – The shape shifting of Faifne the poet and his sister Aige
Type of Spiritual Experience
A description of the experience
The Fairy-Faith in Celtic Countries, by W.Y. Evans-Wentz, 
In the Rennes Dinnshenchas there is this passage showing that spirits or fairies were regarded as necessary for the employment of magic:--
'Folks were envious of them (Faifne the poet and his sister Aige): so they loosed elves at them who transformed Aige into a fawn and sent her on a circuit all round Ireland, and the fians of Meilge son of Cobthach, king of Ireland, killed her.'
A fact which ought to be noted in this connexion is that kings or great heroes, rather than ordinary men and women, are very commonly described as being able to shift their own shape, or that of other people; e. g.
'Mongan took on himself the shape of Tibraide, and gave Mac an Daimh the shape of the cleric, with a large tonsure on his head.'