Okay so my title is reaching. I don't know what you have or have not heard of, but that's okay. I am still going to give you a list of some of the more usual ones that are tempting to use in a story.
1. Clurichaun: This awesome creature is kin to the leprechaun only they are more curmudgeonly and they guard wine cellars. This is my kind of supernatural creature.
2. Leshi: This supernatural baddie will do the unthinkable. He will take you to his cave and tickle you to death. That's right, friends, we have the tickle monster all the way from Slavic mythology.
3. Lady Midday: Now this one is a weird one. She will question workers at noon on hot days, asking them very difficult questions. If they do not get them right she chops off their head. I believe this was how employee evaluations got started.
4. Dullahan: This is a headless horseman, but not quite the one Washington Irving imagined. This one carries it's own head under one arm and a human spine in the other hand to use it as a whip for, you guessed it, his horse. But that isn't the end of the grotesque details. The head also always have a smile and the eyes move around in it. All I can say if they should have reached further on the headless horseman.
5. Bakhtak: I like this one because I have lots of nightmares. This heavy little dude climbs on you while you sleep and makes you have bad dreams while also causing sleep paralysis.
Okay, that's my list!