* You were forced to kill your family friend. Your own wife and child have become ravenous, flesh-eating ghouls, as have thousands of people across the West. Once serene (well, for the most part) settlements have become fortresses against the shambling hordes, their residents dwindling in numbers. Ammo, as well as allies, are scarce. And you've got to set out into the deadly, zombie-filled land to find a cure and possibly save who you can. And those animals that gave you such a hard time in ''VideoGame/RedDeadRedemption''? They're zombies now.
* Some of the random events you can come across are pretty unsettling. From a group of undead devouring a pile of corpses, civilians transforming right before your eyes, deranged cannibals who invite you for a "bite" and turn their guns on you if you decline, and more. One of the more disturbing ones is coming across a sobbing man sitting next to a dead man, likely a friend or relative. The dead man rises as an undead and the living man is forced to shoot him...[[DrivenToSuicide right before turning the gun on himself]].
** A similar event happens in the vanilla game, only it is possible to shoot the gun out of the living man's hand before he kills himself. This gives you [[KarmaMeter a small bonus to your Honor rating]] [[CrowningMomentOfHeartwarming and feels very good too.]]
* New Austin and West Elizabeth feel ''very creepy'' this time around. The setting in Red Dead Redemption had many merchants, bandits, and deputies to populate the area, but in Undead Nightmare, the only thing your going to see is shambling undead clawing at your horse. Any survivors you see are probably stranded in their homes or are trying to navigate the landscape without being eaten.
** It's even worse at the start of the game, where there's less zombies and less ammo. You don't know what's around the corner, your horse died, you're out of ammo, and... [[OhCrap what are those shadows out in the plains?]]
* After you clear out Blackwater, a group of people are discussing their current situation, when an extremely skinny zombie walks up to one of the women and kills her from behind. It may catch you off guard so once you get a chance to shoot it, its already chewing on you.
* While the characters for the most parts plays the horror of living in a ZombieApocalypse straight, there are some rather... odd instances where John will watch a close acquaintance (such as [=McDougal=] and [=MacKenna=]) get eaten alive right in front of him ''while he does nothing but stand and stare'', and another scene has him and West Dickens witness a man being surrounded and mauled, to which they react as if they just saw someone falling off a bike.
* Tall Trees in Undead Nightmare is easily the scariest area in the game. Terrain is rocky, trees get in your way when you travel, [[BearsAreBadNews zombie bears]] roam here as do zombie wolves. Think you're safe on your invincible zombie horse? You are until a [[FragileSpeedster bolter]] you can't see [[OhCrap pulls you off your horse]] in the blink of an eye to make you a meal for zombie animals. Plus sasquatches lurk here and while they are harmless they tend to let out a [[HellIsThatNoise bloodcurdling scream]] or start talking in a panicked voice that is also pretty scary. And the worst part is that it is so dark you can't see a damn thing [[NothingIsScarier which makes not being attacked terrifying]] plus you're now left shitting yourself wondering [[ParanoiaFuel when you will be and from what direction or distance]].