This is a goat-deer, which is a creature I invented for our gaming group's recent playthrough of Ryuutama. It only lives in a remote village, and each generation one is born soul-bound to a unique child. These children are almost exclusively born with supernatural abilities, and can see into the future in a limited capacity.
Because of this, they have a close tie to the current royal family, who takes these individuals to serve as court advisers when they come of age. The current rulers were able to take control because of their ties with the seers, and thus the royal crest shows the horns of a goat-deer supporting the crown.
The goat-deer is quite large and strong, but less than ideal for riding because of its sloped back. (Possible, but not comfortable or easy.) Their horns are large and quite unique. The goat-deer is hardy and highly intelligent-- under special circumstances they are able to take on another form, assuming the guise of a human from the waist up. Like a goat, they are browsers with a strong digestive system. In addition, they are extremely sure on their feet and have been known to scale sheer cliff walls.