Spirit derives from Scandinavian mythology.
Fossegrimen is a fiddler playing water spirit or troll in Scandinavian folklore and he's associated with rivers, particularly with waterfalls (foss in Norwegian).
He's related to Nøkken (both are water spirits, but Fossegrimen are unable to change his appearance).
If you leave an offering in a waterfall or water a Thursday night he will show up and teach you how to play it. Consequently making you a master fiddler yourself!
If you are to provide an offering. Keep it mind that he prefers black animals. Everything from black cats horses or beetles. In some variations of the myth, you can promise him divine salvation.
Guardians protects its summoning location. Good for Places of Power and Portals.
Summoning ingredients requires: Oakmoss and Harp Strings