This list of mythical creatures that begin with this letter and I am constantly gathering information from each continent, and is continually being updated.
Coblynau (Welsh)
Coblynau are mythical gnome-like creatures that are said to haunt the mines and quarries of Wales and areas of Welsh settlement in America. Like the Knockers of Cornish folklore they often help miners to the richest veins of ore or other treasures by their peculiar knocking sound. They appear dressed in miniature mining outfits, work constantly but never finish their task.
They are said to be half a yard (1.5 ft) tall, very ugly, but often friendly and helpful. When they are angered they cause rock slides. The word Coblynau is related to the English word Goblin and may derive from a Germanic source akin to the German Kobold, via the French Gobelin.