Yes, they are semi-mythical amongst the fey community. They are known to spring forth when an immortal faerie is killed to gain vengeance. They are known as brutal, full of hatred and fear-inducing. The description given by Sterren doesn't quite match the illustration of beings comprised soley of grief and fury, but the reality of things is often that way.
Fearsome hunters and fighters, implacable enemies and unlikely to ever give up voluntarily