Kappa

The Kappa is a Japanese water demon. It resembles a scale-covered monkey with webbed hands and a water-filled depression on top of its head. The water in this hollow is the source of the creature's strength. Kappas live in shallow water. They prey on the blood of humans, strangling anyone unlucky enough to wade into their ponds and rivers. However, a person confronted with a Kappa can do something to protect themselves, either by appeasing the creature or outsmarting it. A Kappa will not attack a person if it is thrown a cucumber inscribed with that person's name. It can also be tricked into bowing, so that the water spills out of the hollow on its head, rendering it powerless.