Mycelium is a fae wolf. One of many in Die Nachtkinder. Not fae in the human understanding of the term, but the true primordial sense. He is... well, was Manetheren's understudy. The old, grizzled moonlit wolf taught the young fae to be one with the trees, moss, mist and mud of their territory.
Selkie befriended the wanderer early in her reign as Alpha of the Nachtkinder pack, and instilled in him the importance of living as true wolves should.
It was a v sad day when Manetheren passed away, but Mycelium was ready to take his place in the pack.