Mythological Beings

Like The Broken Sword, The Merman's Children assumes that each national mythology accurately describes non-human intelligences that once existed in that country. Thus, in the fourteenth century:

merfolk had colonised various coastal waters;
a were-seal dwelt at sea but alone;
Leshy tricked people in the wildwood;
polevik kept blight from crops;
domovoi embodied a household and its well-being;
Kikimora sometimes helped housewives;
a vodianoi, growing old or young with the lunar phases, was a water monster shaped like a bulky man but covered in moss and weeds, tailed, webbed and taloned;
a vilja was a young woman barred from Heaven because she had drowned herself, now embodied in mist, wind and dreams, pulling men underwater if they embraced her;
Rousalka, further north, were similar to but more fearsome than vilja;
a tupilak was a stuffed walrus hide with sewn on fangs and claws, animated to move, seek the water and prey on its maker's enemies. (There was an animated creature in Oz: the Gumph?)

I had previously heard of only three of these ten and had encountered the term Leshy only because Larry Niven used it in the title of one of his series.