The Beast of Bodmin Moor is a great story, although I think that that may be a large black cat. Mermaids feature in Cornish stories which makes sense, Cornwall is often coastal or at least, some of its best features are. Selkies possibly, women who become human when they remove their skins who can be stolen away by mortal men. Cornwall also has fairies which come in a great many varieties, such as piskies, spriggans and knockers. The knockers are associated with stories revolving around the old, abandoned tin mines of which there are many littered across the Cornish landscape. I once saw the story of the Cutty Black Sow in an episode of Tales From The Dark Side, where a young boy is trying to help his dying grandmother by placing stones with names on within their hearth fire; it doesn’t end well as some stones happen to fall out, which as we know means trouble for the Cutty Black Sow will catch up with you, and he does.