The glashtin is fabulous creature and a shapeshifter in the folklore of the Isle of Man.
Also called cabyll-ushtey, howler, howly, cow-lug sprite.
The Glashtin most frequently appear as either cows with horses’ heads or alternatively as horses with cows’ heads. The bovine headed Glashtin are considered generally harmless and stupid while the ones with the horse head and cow body are thought to be very clever and manipulative. They are generally of regular farmyard proportions, though may sometimes be smaller. In humanoid form the Glashtin either appear as a handsome young man with curly dark hair and sparkling eyes, or as a strange child-like being. Either way their ears will be pointed or like those of a cow or horse.
The Glashtin is a shapeshifter that can appear as a man, an hybrid or an animal (cow or horse). In each form he is incredibly muscular and looking for someone to ride him, a journey which always leads back to the still waters he calls home, where his rider discovers they can't jump from his back, and they get pulled to their deaths. However, glashtins can be put to good use, as farm hands, if you can control them
Glashtin may often be heard rather than seen, however, hence their alternative name of ‘Howlers’. Their eerie cries may have the benefit of warning humans about approaching storms, however the Glashtins’ wailing is likely to arise out of joy not fear and some people suspect that these creatures may actually cause harsh weather. They get very riled up with thunderstorms, and locals do hear them howling as a storm approaches. They're scared of fire and vulnerable to burns.
"In 1859 it was reported that an animal of this kind was to be seen in a field near Ballure Glen, and hundreds of people left Ramsey in order to catch a sight of it, but they were doomed to disappointment. The people about Glen Meay believed that the glen below the wateffall was haunted by the spirit of a man who one day met the Glashtin, or Cabbyl-Ushtey, and, thinking it was an ordinary horse, got upon its back, when it ran off and disappeared in the sea, and the rider was drowned." from Folklore of The Isle of Man by A. W. Moore, 1891
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