A horse that has fallen into the claws of the undead will rise again, becoming an undead horse. The body has been severely decomposed, the head and neck is stripped of flesh, exposing the skull and dangling brain matter. The horse is blind, since its eyes are ripped out. The legs are broken and the body is battered, bloodied, and ribs protrude out the sides. These undead giants are found mindlessly wandering around the lands along with the rest of the undead horde.
Any horse the player owns can become an undead horse. All the player must do is allow their current horse to die; when the dead horse is whistled for, it will return as an undead version of itself.
Undead horses are much faster than their living counterparts and much like the Four Horses of the Apocalypse, they have infinite stamina. However, the undead horse is much harder to control than any other horse and during riding the undead horse will always steer south, making riding difficult.
To counteract the difficult steering of the Undead Horse, always push the thumbstick hard in the desired direction of travel. Also note that Undead Marston can ride the Undead Horse with no steering difficulty but as Undead Marston he will have trouble controlling any living horses.().
Occasionally, a glitch will occur where after a Horse of the Apocalypse dies, the player will always get an Undead Horse.
The appearance of an Undead Horse will often vary. One horse may have more skin than another, or may be of a different color.
Sometimes the game will glitch if the player is riding one of the Horses of the Apocalypse and it dies. If the player whistle, they will get an Undead version of the horse they were just riding. This usually happens with the Unicorn.