The Horse is a riding beast utilized by the Yautja. There is no evidence to suggest that the creatures are used on the Hunt specifically, but the impaled Yautja head may suggest they are used during internal conflicts by the Yautja.
The Horse is a large battle-mount (considerably large considering the Yautja and human size difference), it has a glossy smooth head with no discernible eyes, ears, or nose, somewhat similar to a Xenomorph. It has a red body, a tail similar to that of a horse, and hoofed feet.
Behind the scenes
The original collectible statue that features the Horse was released in Japan by Fewture Models. The model was unpainted and with the Predator rider wielding a gigantic axe. The imported version by Sideshow Collectibles features a completed paint job for the creature and a different weapon for the Predator: a spear with a Yautja head impaled upon it.