Coblynau
Coblynau are mythical gnome-like creatures that are said to haunt the mines and quarries of Wales. They are said to be half a yard (1.5 ft) tall, and very ugly. Like Knockers, they are dressed in miniature mining outfits. They work constantly but never finish their task, and are said to be able to cause rockslides. The word Coblynau is derived from the English Goblin ultimately derived from a Germanic source akin to the German Kobold, via the French Gobelin.[1][2]
Coblynau are mentioned in the Constantine episode "The Darkness Beneath", but the description of the creatures given is closer to knockers.
