Coblynau

Coblynau are a type of small creature resembling gnomes or goblins whose roots lie in the folklore of North and Middle England.

Overview
These diminutive humanoids are said to stand no taller than a foot-and-a-half in height, dress in outfits reminiscent of the protective gear worn by miners, and are exceedingly ugly. Inhabiting the mines and quarries of England, they are highly industrious beings, but are never able to finish their tasks, although whether this is down to them taking on too much work or simply being perfectionists is unknown. They are also believed to be able to cause rockslides and cave-ins; why they would wish to do this is a mystery.