A green man from Czech mythology. It is my understanding that there are lots of Vodniks. They live in the bottom of bodies of water and capture the souls of drowned people in bottles.
There is one folk tale where a Vodnik falls in love with a human woman and gets her to live with him at the bottom of a lake. They have a child, but the woman is very unhappy as she's pretty lonely at the bottom of the lake. To cut a long story short, it's not a marriage made in heaven. The woman leaves under false pretences to visit her mother, taking the baby. She doesn't return. Vodnik is heart broken and very angry. One day, the woman returns to find the bloody ripped up remains of her child on the door step. Yuck!