Grindylow

A Grindylow is a small, horned water demon that lives in the weed beds at the bottom of lakes in Great Britain and Ireland. It has green teeth, pointy horns and long fingers, which are used to strangle their prey. They are violent and aggressive towards wizards and witches and Muggles, although merpeople  have been known to domesticate them and keep them as pets.Grindylows inhabit Black Lake at Hogwarts School of Witchcraft and Wizardry, and they attacked students competing in the 1995 Triwizard Tournament, forcing the retirement of Fleur Delacour. In Harry Potter's third year at Hogwarts, Remus Lupin tells Harry that the trick to combating them is to break their grip; their abnormally long fingers are strong but very brittle. Grindylows mostly survive on fish, algae, and small sea creatures. They are usually not a threat but have been known to eat humans, for this reason Grindylows are considered 'Dark Creatures'.