The Dark Horse has a slick black body, white face and muzzle, and blood red eyes. Its body is covered with unexplained scars and wounds.
While it has an average speed on par with most mid-tier horse breeds, the Dark Horse is notable for not losing speed if it runs off-road. Its health and stamina are also noted for being higher than most horse breeds, making it a durable mount in combat.
The Dark Horse is a unique horse breed available for Marston if the player's Honor is at its lowest level. Should the player whistle while not having any other horse called, the Dark Horse will arrive as Marston's mount. If it dies, the Dark Horse will respawn after an in-game day.
If Marston's Honor will raise to neautral or good, the Dark Horse will stop responding to the player's whistling, even when saved at a hitching post.
- Setting up a campsite then traveling from it may glitch the Dark Horse, causing it to lose its saddle and act like a wild horse. When the player whistles, a saddled Dark Horse appears.
- The player will receive the following message after earning the honor level of Road Agent, thus receiving the dark horse: "Your honor has dropped low enough that a dark horse has responded to your whistle. If your honor goes back to neutral or above, you will lose this rare mount."
- The Dark Horse is not the same color of black as the War Horse. It is actually a minimally expressed American Paint Horse (minimally expressed means there is a very small amount of white, such as across the face).
- Due to its powerful and chunky build, it could possibly be a type of draft horse, which are horses used for manual labor.
- If the Dark Horse is used in a mission where another character has to be followed on horseback, depending on how fast the character rides, the Dark Horse will not be able to keep up. It is a good idea to either break a wild horse or, being with low honor anyway, steal a horse before beginning such a mission.
- Sometimes a glitch occurs, and when the horse is called, two come rather than one. This can also occur with the War Horse.
- A good way to keep the dark horse is to put on the bandana so that positive actions don't increase the player's honor.
- This mount is considered rare because the player can only obtain it by having a very low honor level.
- If you abandon the horse, kill the horse or break and/or hitch any other horse regardless of what it is, if you whistle for it, another dark horse will respawn.
- If the player is wanted, the Dark Horse's ability to run off-road without a drop in speed allows the player to quickly lose their wanted status.
- The Dark Horse's design may be a reference to the western "3:10 to Yuma" (2007), as an identical horse with a mirror image face stands out in the movie. (Picture below in Gallery)