The first demihuman race for my campaign is the Nisse. They are named after one of the magical creatures my grandmother used to tell me stories about. I think there was a little song she sang at Christmas time but I don't remember that. It was in Norwegian which I no longer even understand much less speak (to my shame I tried to sing some of the songs and I couldn't even finish the ABC's). *hangs head in remorse*
Her stories of the Nisse are more complicated that the other stories of trolls, giants, witches, and stuff. A Nisse might be a little creature (I imagined them as three feet tall or so) but they were as strong as a strong man. While they were secretive and shy, they were intricately tied to a farm. Even though they might live in holes in the ground, they were attached to the local farm/s emotionally and in some ways physically. A Nisse enjoyed a prosperous and orderly farm. If there was something out of place, a Nisse was not happy. Expect to find the cow's tails liberally dipped in manure, hay stacks moved from one field to another or even taken to the neighbors and the horses tired with tangled manes in the morning.
A contented Nisse would see cows giving good milk, the beer (which my great grandfather brewed on a 'dry' reservation) would be tasty and frothy, the horses would be content with gleaming coats and shiny manes and tales from all the extra attention they got at night. Manure would be easier to clean, fields more fertile etc. The point was that Nisse like an orderly farm and would act accordingly.
As a character race I see them as a race of people who are much like the farmers of Norway. Nisse would love well cared for fields and gardens, a neatly kept (underground) house, outbuildings, sheds, and barns. In my campaigns adventuring Nisse would fit into a kind of fighter, cleric, or thief role. Non-adventuring Nisse would live on farms either in their own villages or sharing a farm with the 'big folk'. I see them in a privileged, tenant class on the farms that they work for 'big folk'.
Nisse are small sturdy folk between three and three and a half feet tall with work roughened red hands and weathered faces (the men more than the women). The men grow short beards after they reach one hundred and fifty or so years old. They have light blond to light brown or red hair, and blue or green eyes. Nisse live for hundreds of years especially if they live on an active and prosperous farm. If the farm they are emotionally attached to becomes rundown over time the Nisse will also begin to 'age' eventually becoming a haggard, angry creature, skinny and bedraggled with thick tangled graying hair and beards.
Male Nisse dress in an over tunic, under tunic belted at the waist with draw string trousers or leather britches, heavy farmer's boots. Most men dress in blues, browns, or greens or in undyed wool. Female Nisse wear a long outer tunic, an inner tunic, pinned at the front at both shoulders and belted with a leather or woolen belt. They wear low boots and shoes. The women wear a colorful inner tunic and light outer tunic.
In nature, Nisse are calm cheerful people with a good work ethic and strong desire to see things in their proper place. Adventurous Nisse are looked upon as not quite respectable as they do not stay in their proper place and fit in with the rest of the community. In a Dungeon World campaign they might be a subset of the Halfling race. They would fit nicely there.