The ceffyl dwf is the Welsh Water-horse, very much like the each uisgue of the Scottish Highlands.
The Ceffyl Dwfr is generally described as a beautiful but small creature who is seen grazing at the banks of a stream or waterway. It may tempt the unwary traveler to mount him at which point it will soar into the air and fly over river and mountain before suddenly melting into thin air to throw his rider to destruction upon the ground far below. Some versions of the Ceffyl Dwr are said to be luminous.
Though more commonly associated with fresh water, there were versions of the ceffyl dwr who frequented the sea shore. These were often described as being dappled grey, or were sandy brown in colour and it was said that they could be identified because their hooves faced the wrong way.
It is said that a man once caught a ceffyl dwr on the shores of Bae Ceredigion and aftewards he tried to break the creature to the cart. By means of an artfully contrived bridle he led the animal home, and used it as a cart-horse. But one day the bridle became unfastened, and the ceffyl dwr darted with the cart and driver into the sea, and was never seen again.
Ceffyl dwr, in the form of a huge and clumsy horse were reputedly seen plunging up and down in the sea when thunderstorms were brewing, or just before a gale and the colour of its coat would reflect the weather conditions, changing from the pure white of sea-foam to the slate grey of thunderheads. It is said that a St Bride's Bay just after a storm such an animal was seen. Somehow a local farmer managed to catch it and put it to the plough. This arrangement seemed to work for several weeks until one day, seized by some internal impulse, the ceffyl dwr turned and dragging both plough and ploughman behind it reached the shore and plunged headlong into the sea, to be lost amongst the waves.
In parts of Gwynedd it was believed that the merlynod, small steeds peculiar to the area, were sired by the ceffyl dwr on mountain ponies. Tales told in the region also suggested that the ceffyl dwr could transform itself into other creatures and this it became a terror of the night. Often it would change into a goad and rush at its victims, causing them considerable injury.
In neighbouring Clwyd it was believed that the ceffyl dwr would transform into a frog and leap upon the backs of its victims, clasping them in a fiendish embrace. Tales of ceffyl dwr transformations were not confined to the north, however. For it is said that a man living in the wilds of the Rhondda was riding down to Pontypridd early in the nineteenth century, when a Ceffyl-dwr, in the form of a squirrel, leaped between his shoulders. The creature clasped his neck so closely as to make the man gasp for breath. Then he was shaken and beaten so badly that the next day a mysterious illness assailed him from which he never recovered, but lingered on in misery for nearly two years.
A story about the Ceffyl Dwr comes from Glyn Nedd (The Vale of Neath). A man who had been on a long journey lingered there to rest by the shady lee of a large rock near a waterfall. A ceffyl dwfr slowly emerged from beneath the foaming cascade of waters, shaking the river spume from its snow-white mane and began to ascend the slope on which the tired traveller rested. Standig in the sunlight the animal whinnied, snorted and tossed its mane, as if to draw attention to itself.
Seeing this fine animal the traveller was tempted to mount the creature and when he approach the horse came towards him rather than shying away so he was easily caught and mounted. Soon the trveller was safely astride the noble little horse. Though he had no saddle or bridle his hands felt comfortable intertwined with the animals' mane and it seemed a gentle beast. Soon however the passing landmarks indicated that they were travelling at remarkable speed and looking down it seemed that the horse's hooves were somehow not even touching the ground.
For a while at least the rider enjoyed the sensations of travelling so fast but after a while, as the steed's progress did not slow he became alarmed and then terrified. The moon was full in the sky when the steed simply vanished from beneath him and he was thrown to the ground. The shock of the fall was very great and he lay there dazed and bruised for a long while. At dawn the man picked himself up and dusting himself down he walked down the slow until he came to the town of Llanddewi Brefi, Ceredigion, many miles away from where he had started.
Another story about the Ceffyl Dwr comes from Aberthaw, Morgannwg. During the early part of the nineteenth century an old man found himself walking down the moors near Aberthaw. It was a cold night near the midwinter solstice and as dark low-lying clouds threatened to obscure the moon the old man quickened his pace, fearing that snow would soon come.
When he was at about the mid-point of his journey he was astonished to see, about a stone's throw ahead of him, a small horse ridden by a gangly long-legged man. Horse and rider both were outlined by a dim shimmering light. He sought to catch-up with the traveller but no matter how he quickened his pace the little steed somehow seemed just to out-distance him. Then, just as he reached his destination the figure and his steed slowly vanished.
As he related his tale to the people of the household they informed him that he had seen a Ceffyl Dwr. That same night the valley through which he had been travelling was flooded by an unusually high full-moon tide and ever after he attributed his escape to the guidance of that little glowing horse.