I won't pretend to be an expert on these Slavic fey—Eastern Europe is where my grasp of folklore gets fuzzier. But all three of these house spirits—the domovoi, dvorovoi and ovinnik—are charming wee folk with a lot of character. They exhibit all the helpfulness of a brownie—well, the domovoi does, at least—and two of the three have the power of foretelling. That’s quite a boon if you can convince the fey to grant it…but the transaction is not without risk. Speaking of which, all three house spirits also have some personality quirks that make them highly entertaining as NPCs, but quite troublesome as adversaries if they ever go a bit…wrong.
And so, while in the main these are mostly harmless and sometimes even helpful spirits, it’s that whole “gone wrong” bit I’ve emphasized in the adventure seeds below… I mean, who doesn’t love pyromaniac cat-faeries?
A parsonage has long been blessed with a domovoi. Some members of the family even suspect he is a reincarnated ancestor, or a household god from the time before the Azure Crusade. But the family’s overreliance on the domovoi for auguries, as well as the Aklo-laced whisperings of a neighboring witchcrow, have driven the old fey mad. He has become a barabashka, a knocker, using mage hand and telekinesis to hurl objects about and rap on the walls. Unless restored to his old self, it is only a matter of time before he does real injury…or worse.
An adventuring party’s wealthy benefactor has a beautiful new wife…until, thanks to a polymorph lobbed by an old enemy, he suddenly has a beautiful new white cat. The adventurers aren’t ready to take on the evil wizard yet, but they can try to keep the cat-wife in good health till a dispel magic can be arranged. That won’t be easy, as the benefactor’s estate is watched over by a pitchfork-wielding dvorovoi, and the wild fey takes an instant (and murderous) dislike to the snow-white feline.
In Brementon the night is split with the howls of angry animals. The cries are of such ferocity that instead of brandishing brooms and throwing stones to hush the creatures, the Bremenfolk instead lock their doors and shy away from the windows. In daylight, they whisper of “the Dog War.” Actually it is a war between house spirits and gremlins, the catlike ovinniks and the doglike pugwampis. Driven from their canyon homes by filth, disease, and other monsters (including a possible looming invasion of flinds), the pugwampis attempted to move into Brementon en masse. The local ovinniks are having none of it, but they don't have the numbers to rouse a proper defense against the gremlins, resorting instead to guerilla strikes. As the conflict wears on, the collateral damage is beginning to grow. The ovinniks have begun attacking anyone they regard as a pugwampi sympathizer, including harmless dog owners, and they have burned down a handful of houses they suspected of being gremlin-infested. Meanwhile, the ill luck manifested by both sets of fey has settled over town like a miasma, spoiling milk, ruining cart axles, and generally making life miserable.
—Pathfinder Adventure Path #67 86–87 & Pathfinder Bestiary 5 142–143
Actually house spirits versus gremlins is kind of a thematically perfect adversarial setup, and throwing 1st-level PCs in the middle could be a great campaign kickoff. If you’ve got players who really like playing monsters, you might even skip the core races entirely and have the PCs start off as fey. There might be some balance issues early on, but Pathfinder offers some guidelines for doing so. (As a bonus, 3.0-era D&D had a whole book on the subject, Savage Species. Normally I don’t recommend rule-heavy splatbooks, but you might find this one useful.)