One of the more unsettling spirits I’ve read about is the poludnica, also known as Lady Midday or the Harvester of Souls. You find her all across Eastern Europe, under a variety of names. Usually it’s poludnica or poludnitsa or something similar. Most folktales describe her as looking like a tall young woman (though some describe her as an old crone or a child), thin and stately as a stalk of barley.
You see, the poludnica is a harvest spirit. One doesn’t generally think of Russia for its summers, but the heat in the fields can be as dangerous as the fiercest blizzard. During the height of harvest season, in many Eastern European regions, farmers and peasants used to stay out of the fields during the hottest parts of the day, because sunstroke was a very serious risk. The poludnica embodies that danger.
If a person were to go out into the fields during the forbidden hours, they would find her drifting through the grain, dressed in white, sometimes carrying a scythe, sickle, or shears. She seems beautiful and serene, but if she catches you in the fields one of several things (depending on the story) might happen. Often she says nothing. Sometimes she’ll pose you a riddle, or ask a strange and difficult question. If you can’t answer the question or riddle you’ll be in trouble, but if she says nothing you’ll be in trouble regardless. The poludnica can cause insanity and illness in anyone she meets, but more dangerous still is her strength. Though she looks frail as a twig, she is strong enough to twist a man’s head right off his neck, or break every bone in his body with her dainty hands. Afterward, she’ll disappear back into the wheat field.
The poludnica doesn’t appear in fiction that often, though there is a piece of classical music by Dvorak based on her, called The Noon Witch:
In your own writing you could use the poludnica as nothing more than a superstition, convenient for reminding the fieldworkers not to risk the noonday sun and scaring children away from important crops. You could use her as a sphinx, with her blocking a character’s path if they don’t answer her bizarre queries. Or perhaps she’s just a fearsome monster, haunting the fields to punish those who trespass during the sun’s zenith. It might also be interesting to go into who she is or where she comes from; female spirits in Slavic folklore, even the monstrous ones, are often the ghosts of women who died prematurely. The fact that she appears as a child, a woman, and a crone is also reminiscent of many triple goddess figures throughout the mythologies of the world.
Though perhaps it’s best not to delve too deeply into her background. The poludnica is an intriguingly mysterious being, and half the fun is in wondering.
Ogres vs Trolls 
thats cool