A marginally-sane magician and prophet who was encountered by Arthur in a late Breton text.
Guynglaff roamed the woods and spouted cryptic prophecies, identifying him with Merlin. Most of his prophecies involved tragedies to befall Britain in the sixteenth century.
Source
An Dialog Etre Arzur Roe d’an Breounet ha Guynglaff | Late 16th century or early 17th century