|Hold it right there, outlaw!|
This article is littered with spoilers, so I reckon you might ought'a mosey on down the road if you don't want to read any plot details.
The outfit is unlocked after completing the Undead Nightmare campaign. It appears to be the bloodstained remnants of the Elegant Suit, minus John's hat and the suit jacket, along with a ragged red headband. After this outfit is unlocked, the Undead will think Marston is one of them and not attack right away, but will begin attacking once John gets close enough. However, even though he has a zombified appearance, humans will not attack him. Unlocking this outfit will also change all of John Marston's quotes to snarls and ragged snorts or grunts. Oddly, NPC's will still understand him, as in the case of a greeting or acknowledgement of another character's statements.
- This outfit appears to be the tattered undergarments of the Elegant Suit.
- This is one of the eleven outfits that are missing John's iconic cowboy hat. The others are the Reyes' Rebels Outfit, Union Suit, Treasure Hunter Outfit, Deadly Assassin Outfit, Savvy Merchant Outfit, Expert Hunter Outfit, Gentleman's Attire, Undead Hunter, Legend of the Apocalypse Outfit, and the Bureau Uniform.
- The Undead Cowboy Outfit is the only outfit to feature the bandolier once the main story has been completed.
- At the end of some pre-release trailers for Undead Nightmare, the "Zombie John" artwork prominently featured in the DLC shows a zombified Marston wearing the Reyes' Rebels Outfit and headband in place of the in-game model's vest and tie.
- After getting this outfit, the player will be unable to change into any other of John's regular clothing. The player may only use either the Army of the Undead or Legend of the Undead outfits, which remain the same as with the regular John Marston model, albeit with a different skin tone and Zombie Marston's head model.
- Equipping the Undead Cowboy Outfit and activating the "Hic" cheat will lead to some hilarious results, such as when you fall over, Marston will attempt to stand up but fail, perhaps because of the way his stance has changed. He will sit up half way but collapse, all the while making noises of pain.
- In multiplayer mode, when using the Undead Marston character, the player may occasionally be spawned as a slight variant. The skin is similar Undead Marston but it resembles more of John Marston as his eye is no longer missing, and they are instead both blood red. And he regains his original Cowboy Outfit. But excluding the hat.
- John wears this exact same outfit (but clean and without rips, and with no headband) on the cover for the original game and some art work, right down to him not having his hat which he otherwise never takes off. This might suggest that this outfit was originally intended to come out with the original game, but was cut off for unknown reasons.