In Manx folklore the Glashtyn is a water horse similar to examples in Celtic tradition and folklore, especially in Scotland and Wales. This particular creature often appears as a dark, splendidly handsome young man, with flashing eyes and curly hair. However, he may be distinguished from a real human being by his ears, which are pointed like a horse's.
A typical story is:
A girl was left alone in her cottage when her father went to market to sell his fish. He told her to fasten the door and not to open it until he knocked three times. She was not at all frightened at first, but when a great storm began and her father had still not returned, she began to be anxious. At last, very late at night, there came three knocks on the door. She ran to open it and a stranger came in, all drenched and dripping. He spoke in a foreign language, but through gestures he asked to be allowed to warm himself by the fire. He would eat nothing she offered him, but laid down by the fire and fell asleep. Soon the lamp went out, but the girl cautiously blew upon the fire until it was bright enough to see the fine pointed ears of the stranger. At once the girl knew that he was the dreaded Glashtyn, who might at any moment take upon him his horse's form and drag her out to sea and devour her. If only the red cockerel would crow from the dunghill. She sat as still as a stone throughout most of the night until one of the peat logs blazed up with a crackle and the stranger awoke. He sat up and drew out a long string of pearls from his pocket. He dangled these before the girl and invited her to come away with him. But the girl pushed them aside and at that the Glashtyn tried to seize her. She screamed loudly, and the little red cock, thinking it was dawn, woke and crowed. The Glashtyn rushed out and she heard the sound of his hooves as he galloped away. Slowly the daylight returned, the storm blew out and down by the shore the girl heard her father coming home.—John and Caitlin Matthews , The Element Encyclopaedia of Magical Creatures