Ceffyl Dŵr

This Welsh water horse has the power not only to shape-shift at will, but also to fly. Some people say one can feel when Ceffyl Dŵr is nearby due to its foreboding presence and that you must never look into its fiery eyes, whereas others say he is purely a cheeky pest who playfully swims in mountain pools and over waterfalls.

It is said that if you approach Ceffyl Dŵr, one of two things will happen - either it will evaporate into the mist, or it will jump out of the water and trample you to death.

Origin: Welsh
See also
Kelpie | Myths and Legends