Griffons were fast friends to the Fir'Bolg. The Fir'Bolg could control them and used them in the fight against the Dark. In Forest Heart, right before The Deceiver picks up the Tain, a Griffon can be seen inside a giant tree. Whether this is Durak or just a regular griffon is unknown. It seems weird though, griffon's are more native to the Ermine and not Forest Heart.