Hateful Scandinavian Christmas Elves? I’m in! From Atlas Obscura:
Nineteenth-century depictions of the nisse show a child-sized, bearded man in a pointy red cap, the traditional garb for farmhands. Yet earlier portrayals were much more monstrous. In an illustration from Olaus Magnus’s 1555 book, A Description of the Northern Peoples, a demonic-looking creature sweeps a barn. Tangherlini notes this may be one of the earliest known illustrations of a nisse.
A family that wanted to stay on their nisse’s good side could offer him a tasty present. On Christmas Eve, before the harsh winter had truly set in, farmers left a bowl of porridge in the barn. Everyday porridge was made by boiling barley, rye, or oats in water. But the nisse received something special: a luxurious, sweet porridge of rice boiled in milk and topped with butter.
Woe to the person who forgot the nisse’s butter. In one story, a milkmaid decides to play a trick on her farm’s nisse, hiding the butter beneath the porridge. Seeing his offering ungarnished, the nisse flies into a rage and kills the family’s cow. When he finishes his meal and realizes his mistake, he “solves” the problem by stealing a neighbor’s cow and delivering it to his family’s farm.