In Scottish mythology, the glaistig is a half-woman, half-goat water spirit. She is usually blond and wears a green dress to disguise her goat’s legs. In some stories she is malicious, trowing travellers off course or luring men to her lair to drink their blood, while in other stories she is a benign protector of cattle and herders.
Also occasionally a benign protector of children, from what I’ve read. There may be some connection between her and the Cailleach. Though that word simply means “old woman” or “hag” in modern Irish and Scottish Gaelic, that diminishes the figure greatly, as she was (is!) a goddess in her own right. A diverse one too, dealing winter, the harvest, or the protection of animals depending on the area where she was honored—and feared.
(From The Oxford Dictionary of Celtic Mythology, James MacKillop)
I read this all yesterday because of reasons. And goats.