The Welsh variety of the Cornish knocker. Coblynau are said to haunt the mines of Wales rather than help, but there are some cases where they too have guided miners to ore, when shown the proper respect.

A coblynau is half a yard tall (1.5 ft) and hideously ugly. They wear miners clothes, carrying tiny work tools and lamps, but despite all their effort their tasks are always left unfinished. When they are angered they cause rock slides.