Kappa

Child-sized, green, beaked, shell on its back, webbed hands, and a shallow dish set into the top of its skull that holds a little water. The water is its strength and its life, and it must be kept level. Everything else about the kappa follows from this: the careful way it moves, the way it will not run, and the reason it is so scrupulously, helplessly polite. A kappa that is bowed to must bow back. It cannot not bow back. It will do this knowing exactly what will happen, and then it will lie in the road, empty and courteous and finished. It likes cucumbers more than it likes almost anything, and it will accept one with the same formality it brings to drowning you.

Drag to the River: bludgeoning, melee 5 ft, +3 to hit, 1d8+2, and it pulls toward the nearest water. Sumo Challenge: on its first turn it formally challenges the strongest-looking creature present to wrestle. While the challenge stands it will attack no one else. The challenge is resolved either by wrestling it or by refusing aloud - refusal ends the challenge, not the encounter, and from that round on the kappa fights everyone freely and will not offer that creature a second challenge.

The Dish: while the dish holds water, all of the above. If the water is spilled, the kappa drops to 1 HP, cannot attack, and cannot move more than a few feet until it is refilled. Returns the Bow: any creature that bows to a kappa - genuinely, fully, from the waist - is invariably bowed to in return, which empties the dish. It knows what the bow will cost. It bows anyway. A Service Owed: a creature that refills the dish is not harmed by that kappa again, and is owed one service - a river crossed, a drowned thing recovered, a ford named. It pays what it owes.