Footnotes, [?], are always in Norwegian, but included for those who can use them. The links always lead to English sources.
Trollfolk (troll-people) and huldrefolk (huldre-people)The story I always heard was that the "troll-people" or "huldre-people" were the children of Adam and Eve. One time Eve was washing her children before a visit from God, but she didn't have time to clean them all. Instead of showing God dirty children, she hid them away. God noticed, and told her that those hidden should remain hidden. Because of this, huldrefolk are also called "the hidden people" or "those living under ground" (de underjordiske).
Sometimes the huldrefolk are a wild bunch that kidnaps maidens, sneak into weddings or make mischief in other ways. They can be harmful or just annoying, but when they are harmful their methods are equal to that of åsgårdsreia (Norway's version of the Wild Hunt), where they can snatch people away from their homes or chase them into their deaths.
There are many different kinds of huldrefolk and they vary all over Norway and Scandinavia. The stories written here are those I've heard in Telemark, or read about. When I know of any differences, I will note them, but I'm always open to add more information to this. Just let me know about any variations in the comments!
TrollFirst of all, we have the common Troll. He's always male, always huge and pretty stupid. In the fairy tales, Askeladden can usually trick them into giving away their eyes or cutting up their stomachs, killing themselves. A troll can smell the blood of Christians, which he hates as people, but love to eat.
A common troll turns to stone in sunlight, and several Norwegian mountains are said to once have been trolls. Large boulders are usually said to be thrown there by trolls who fought each other.
They have extremely long noses, tend to kidnap women who either has to be saved by their beau or save themselves (one sends herself back in a barrel that's supposed to contain fish for her poor starving family, placing fish on top of herself and telling the troll that she can see him wherever he is, so when he tries to peak into the barrel, she tells him off and he thinks she's still at their home, keeping an eye on him.
Dovregubben in Peer Gynt by Henrik Ibsen and his daughter are good examples at later trolls. If you want to read more about trolls, please check out this blog post.
As for other huldrefolk, let's start with the Hulder herself.
HuldraHuldra is a gorgeous woman, a semi-benevolent succubus who can lure a man into the Blue Mountain (where the troll-people live) or just make love to him and have his children, which will later come back to torment him. Where I'm from she's known by being a beautiful woman with a cow's tail, but other places she also got a hollow back (all Swedish huldre has hollow backs, as far as I know), and some are also grotesquely ugly.
A hulder can be bound by a man throwing iron over her head. Usually he throws his dagger, as everyone wore daggers at that time, but anything goes. In some stories, shooting over the hulder's head works the same way, but this is not something I've heard in Telemark. An iron bound hulder will have to obey the man who bound her, and marry him. Most hulders are gorgeous creatures, while some look more trollish. Either way, an iron bound hulder has to marry the man who bound her, and he has no choice but to marry her either.
After being married by a priest, the hulder usually loses her tail. If he treats her well, he will be rich and succeed in everything he puts his hands to. But if he treats her bad she will maim him (often in the leg or thigh, giving him a permanent limp) and flee, taking all her riches with her. There are tales of a hulder straitening a red hot horseshoe and telling her abusive husband that she could have done the same to him, had she not loved him .
The hulder owns a flock of cows, that are the fattest and most beautiful cows you have ever seen.
You can recognize a hulder by her tail, which is that of a cow. If you meet a hulder and notice her tail, she will hate you for it. There are stories of men scratched in the face, or having their eyes clawed out, for seeing the tail and commenting on it. But there are also tales of a man who discreetly told her her tail was showing so she could hide it. He was thanked with a gift from the hulder, which was that he could aways see the huldrefolk.
ByttingThe most gruesome of all huldrefolk has to be the bytting, or "the swapped one". If you didn't protect your newborn, unbaptised child by carving crosses over the door and putting an iron scissor in his crib, he could be taken by the huldrefolk, to be replaced by a gruesome and ugly thing. Both boys and girls were taken in this way, and the only way to get your own child back was to either abuse the bytting until the huldrefolk swapped them back or to trick the bytting to speak. Baptising a bytting would do nothing to it, unlike other huldrefolk who would be transformed or harmed by holy water.
A bytting is ugly, he or she keeps screaming for more food, and never learn to walk. It doesn't take much imagination to see that this most likely was an explanation for how some children were born handicapped. Drowining or harming a bytting was common remedies, although some fairytales speak against this. In one a mother refuses to mistreat or leave her bytting child, even when her husband leaves her for it. After they seperate, she finds her own child in the forest, and he tells her that because she never abused the bytting, the huldrefolk never abused him, and because she was willing to leave her most precious husband to keep the bytting, that choice broke the spell the huldrefolk had over her son.
Another way to get rid of them was by trickery. Byttinger could speak while newborn children could not. I remember a fairytale where a mother pulled up a small spruce and used it to stir her porridge. The bytting watched her do this for a while, then he said "I've lived long and seen much, but never have I seen someone stir the porridge with a spruce." Once he'd said that, he was reviled and forced to give the woman her child back.
Wikipedia's entry on byttings is pretty close to those stories I've heard myself. Because both trolls and huldre are so different from what I've heard, and include all of Scandinavia when the stories vary so much from one place to another, I've usually chosen to ignore those articles.
NøkkenIf you swim amongst the water lillies (in Norwegian called "nøkken's roses"), the Nøkk might grab your feet and pull you under water, where he drowns you.
If you travel to the forest alone, and you're approached by a beautiful white horse, don't ride it. It might be nøkken, trying to lure you onto his back so he can ride you into the closest water and drown you.
Notice a similarity? Nøkken is more of a nature spirit than anything else. He lives in ponds or lakes of still water (never too close to the streams or waterfalls, that belongs to Fossekallen), where his main objective in life is to drown people. He's a shapeshifter, but in human form he's either completely gorgeous or a horrible beast covered in grass and mud from the lake. In that way, he resembles Draugen, a seafaring nature spirit known for his reign over the sea. (I will probably make a post on Draugen sometime later, both because he's a facinating monster and because it will take way too long to describe him here).
FossekallenFossekallen (the man of the stream) or Fossegrimen (the ugly man of the stream) is like Nøkken eiter completely gorgeous or completely horrendous. He lives in streams, usually beneath or inside a waterfall, and is in many ways more benevolent than Nøkken.
Where Nøkken wants nothing more than to be the cause of your drowning, Fossekallen might lure you into his stream to drown you, he might want to do more adult things to you. Where I come from, Fossekallen is usually gorgeous and completely naked, known for being a wonderful musician as well as a nature spirit in his own right. He lures musicians into bargains, where he demands blood or their first born as payment for teaching them to play so beautifully everyone has to dance and won't stop until the fiddler stops playing. In other stories, Fossekallen's music can stop the streams from flowing and the wind from blowing, just so the nature can hear his music.
The wikipedia article about the "Neck" blends Nøkk and Fossekall/Fossegrim, and doesn't seem to realize that Swedish and Norwegian tales aren't interchangeable, so take it with a shovelful of salt as it imo isn't a good resource.