Fossegrim

In Scandinavian folklore, the Fossegrim, also known simply as the grim (Norwegian) or Strömkarlen (Swedish), is a male water spirit or troll who plays enchanting songs on the fiddle, especially the Hardanger fiddle. It can be convinced to teach the skill.

The fossegrim is related to the nykr or nixie and is sometimes also called näcken in Sweden, but is associated with rivers (the Swedish name "Strömkarlen" means "The River Man") and particularly with waterfalls (foss in Norwegian) and mill races. He has been associated with the kvernknurr, a mill spirit.

Myths & Legends
The fossegrim is described as an exceptionally talented fiddler: the sounds of forest, wind and water play over his fiddle strings. The Swedish say the strömkarl 's ("river-man") song is said to have eleven variations, the final one being reserved for the night spirits because when it is played, "tables and benches, cup and can, gray-beards and grandmothers, blind and lame, even babes in the cradle" will begin to dance.

Their songs were known to lure women and children to lakes or streams where they would drown. However, not all of these spirits were necessarily malevolent; in fact, many stories exist that indicate at the very least that nøkken were entirely harmless to their audience and attracted not only women and children, but men as well with their sweet songs. Stories also exist where in the Fossegrim agreed to live with a human who had fallen in love with him, but many of these stories ended with the nøkken returning to his home, usually a nearby waterfall or brook. (Compare the legend of Llyn y Fan Fach in Wales.) Nøkken are said to grow despondent if they do not have free, regular contact with a water source.

Appearance
Fossegrim and derivatives were almost always portrayed as especially beautiful young men, whose clothing (or lack there of) varied widely from story to story.

Teaching the Fiddle
The fossegrim is said to be willing to teach away his skills in exchange for a food offering made on a Thursday evening and in secrecy: a white he-goat thrown with head turned away into a waterfall that flows northwards,  or fenalår (smoked mutton) stolen from the neighbour's storage four Thursdays in a row. If there is not enough meat on the bone, he will only teach the supplicant how to tune the fiddle. If the offering is satisfactory, he will take the pupil's right hand and draw the fingers along the strings until they all bleed, after which he will be able to play so well that "the trees shall dance and torrents in their fall stand still". Jacob Grimm cites a variant in Johan Ödman's 18th-century Chorographia Bahusiensis according to which the strömkarl must be offered redemption or he will merely break his instrument and weep bitterly.

Famous fiddlers who were said to have learnt from the fossegrim include Torgeir Augundsson, known as Myllarguten (who denied it to Theodor Kjerulf) and Ole Bull, whose statue in the centre of Bergen depicts a fossegrim playing his harp under the falling water; the sculptor, Stephan Sinding (1846–1922), intended it to symbolise his being inspired by Norwegian nature and folklore. The folklorist Rikard Berge said that he told the story to the fiddler Håvard Gibøen when they were both boys but that neither believed it.