Hiisi are creatures found in Finnish mythology and folklore. While the word has roots in paganism, it would later be used to describe monsters similar to giants, trolls, or goblins.
Hiisi were believed to be found in promontories, potholes, large boulders, woods, hills, and other rough terrain. They were scared off by cultivation, and thus, in order to escape them, people would flee to cultivated land.
Hiisi could be seen as demonic (especially when Christianity became more common) or magical, with trickster-like traits. Over time, the word has become increasingly associated with evil, to the point it can sometimes be used to refer to Lucifer himself.
Hiisi could be small or gigantic in nature with a wide variety of abilities, most connected in some fashion with the wilderness. They could be solitary creatures or gather in large, noisy groups prone to attacking and harassing anyone that strayed near them. They were also prolific thieves, and would raid any home that left their doors open.