A Bwbach, 'BOO-bahk', is a Welsh House-Goblin. Bwbachod are basically benevolent and will do useful chores, such as sweeping the floor, during the night, in return for a bowl of cream. However they have a mischievous side too and like to play tricks on teetotallers and priests.
As of September 2026 bwbach has been added to the Oxford English Dictionary!