Chiron is an example of a species of half humans and half this animal, which are known as centaurs.  
Rhiannon is said to ride a white variety of this kind of animal. Kelpies, which lure people to their deaths by drowning, are said to resemble this animal. An offspring of Poseidon and Demeter, Arion, was this type of animal. Diomedes owned some man-eating varieties of this animal. Loki changed into this animal and mated with Svaldifari, leading to the birth of an eight-legged one, Sleipnir. Chiron is an example of a species of half humans and half this animal, which are known as centaurs.  For 10 points, Pegasus is a winged type of what animal?
Rhiannon is said to ride a white variety of this kind of animal.
{horse}s [prompt on “mare”; prompt on “stallion”]