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, for its eyes are plucked 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.().
Undead horses actually have slightly more speed than its living breed. If you find an undead Painted horse, its speed will be much higher than a normal Painted horse, but will be slightly slower than say, an undead American Standardbred.
The occasional Undead Horse can produce an "Undead Horse Heart".
Once the player has finished the game, undead horses will no longer steer south and will move like a regular horse. However regular horses will turn south.
Occasionally, a glitch will occur where after a Horse of the Apocalypse dies, the player will always get an Undead Horse.
The Undead Horse might steer south because that is where the mask that started the plague is.
The horse may be performing the will of Ayauhtéotl, pressuring the player south to Mexico so that way they might stop the plague.
The horse may also be trying to go in the direction of the moon.
Marston will often express his disgust of undead horses.
The look of your 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 out if you are riding one of the Horses of the Apocalypse and it dies.If you whistle you will get and Undead version of the Horse you were just riding.This usually happens with the Unicorn.