Ghost people are mutated humans, changed forever by a combination of corrosive rust-like toxins unique to Sierra Madre, known as the Cloud. This same red cloud clings to the walls and lingers like a thick smog in localized areas and even escapes and is reabsorbed continuously from the ghost people's hazmat suit by means of aeration on their legs, indicating that their mutation may well originate from constant exposure to the Cloud. This has resulted in them being the only ones able to walk in and out of the Cloud without any further damage.
The ghost people originate from the construction workers before the Great War who were mutated from the cloud as they worked on the Sierra Madre Villa. They have several ties to inhumane experiments of Big MT. According to data from terminals in the medical section of the Sierra Madre, construction workers at the site first received their hazmat suits specially created in the Big MT after a gas leak sent one of them to the hospital. A terminal in Big MT states that the gas leak itself was also created at Big MT, the hazmat suits being an "experiment within an experiment." The hazmat suit was bulky, nearly impossible to speak through, grew stiff with use, and had locks that, after contact with the Cloud, corroded to the point where the hazmat suit had to be cut open with a cosmic knife, and still didn't provide proper protection from the poisonous gas cloud.
The ghost people have acquired their moniker through their practice of "hunting" the holographic "ghosts" of the Sierra Madre Villa, perhaps seeing them as some reverent figures or prey from which to draw power. Their name can also be ascribed to the ghostly manner in which they inhabit the ruins, their manner, movements, and general presence seemingly much akin to a malignant haunting to any who have survived and fled attempts to breach the Sierra Madre. It is not clear why the ghost people drag their victims off into the Cloud. Whether to consume, torture, or convert them into something like themselves, nobody knows, or has survived to tell the tale.
Ghost people are very mysterious. They do not speak, and they seem to neither sleep nor eat. They seemingly exist only to lurk through the villa ruins, forever seeking prey, whether mortal or holographic; if they have a lair at all, it is unclear where. Although according to Dean Domino they live in the underground service routes and sewers of the Sierra Madre Villa.
They shamble like classic undead creatures. Despite this, they are in fact quite agile when necessary, often lunging and dashing with surprising and inhuman speed. Quite often, they will appear from the shadows to strike or pursue prey relentlessly throughout the region, stopping only once their victim(s) is dead or when they are dead themselves. Despite their apparent lack of mental agility, they seem to be capable of manufacturing crude weaponry out of broom handles and cosmic knives (or at least scavenging them and understanding their purpose) and also have gained the ability to utilize and/or produce throwing spears, which testifies to surprising mental facility and also surprising co-ordination adroitness. Also of note is their use of gas canisters modified into explosives and their successful conversion of bear traps into ramshackle but deadly unarmed weapons. Dean Domino also cautions they can set simple traps by leaving supplies in an area but set a trap for unsuspecting victims. All this points to the ghost people being far more intelligent and insidious than other mutant humans, such as the tunnelers of the Divide and the feral ghouls of the wider American wasteland.
When questioned on how ghost people taste, Dog says that they have pockets of pressurized gas inside them, which explains why blood and yellow fluid spray at apparent high pressure when they are injured. Also, they are immune to fire due to their mutations and despite virtual immortality, they can die if one of their limbs is severed, showing a universal mutation from which everything is connected to each other, not just the brain with the other organs, causing direct death if a member is removed. Oddly enough, similar to Glowing Ones, when they are decapitated the body spews red blood from the wound, instead of the characteristic glowing green blood. Ghost people also scream before attacking, similar to feral ghouls.
Nearly all ghost people are hostile to the Courier. They are difficult to pin down, as they will constantly lurch and jump around during engagements. They also actively avoid a rifleman's aim, particularly near their head. They do not utilize firearms, using only primitive weapons made from resources found in the Sierra Madre villa. Ghost people can be more difficult to kill with firearms than most other opponents, because they do not take extra damage from headshots. This is somewhat balanced by their complete lack of functioning armor.
They are difficult to kill permanently by normal means; they must be disintegrated, dismembered or eaten by Dog, or they will simply get up and continue attacking. The simplest way to keep them from getting back up is to cripple or dismember their limbs with a melee weapon (like a cosmic knife), an explosive (like a demolition charge), or from concentrated ranged attacks to a single limb. The loss of a limb will always kill the ghost person. If a ghost person is already down, attack with a melee weapon or target their limbs with a ranged weapon until a limb is removed to stop them from reviving. Crippling a limb while a ghost person is conscious will dismember the limb, killing them even if the crippling attack does not reduce their health to 0. The Bloody Mess perk helps considerably with this task, since it increases the chance of dismemberment with standard firearms. The revival of the ghost people is indicated by characteristic gurgling, so it is recommended to either stand back or quickly destroy one of their limbs before they wake up.
Often the only warning of their presence is a strangled choking or muttering sound they make. Ghost people are technically exceedingly easy to sneak by, as they have zero Perception, but the narrow streets and many traps around the Villa make sneaking past them much harder.
Ghost harvesters are the most common variant of ghost people. They are the smallest variant and are easily distinguished by their hoods and smaller gas masks.
They are equipped with knife spears and throwing knife spears, using the throwing spears until they are exhausted and then charging the target equipped with a knife spear, unless the prey closes to melee range first.
They are not the most durable or proficient opponent in close combat, but their throwing knife spears can cause great damage in a short time. Also, they usually perform a jump to the right or left after throwing a spear, which makes them hard to target with a firearm outside of VATS.
Ghost trappers can be identified by their large size and lack of hoods. They are only equipped with bear trap fists. Ghost trappers are also responsible for the inordinate amount of bear traps and trip wires in the Sierra Madre.
They are capable and tough unarmed fighters, so they are best picked off from a distance. However, ghost trappers are often found in groups with knife spear-bearing Harvesters or Seekers.
Ghost seekers are the least common variant of ghost people. They are taller than ghost harvesters but slimmer than ghost trappers and usually wear a hood.
They are equipped with knife spears and gas bombs, throwing one or two gas bombs and then closing to attack with a knife spear.
While they do not withstand as much damage as ghost trappers, ghost seekers are extremely capable in melee combat. It is worth noting that the ill-prepared should watch out for ghost seekers, as the gas bombs can cripple limbs.
Ghost people will not set off tripwire-based traps.
It is possible, while in Sneak mode, to see ghost trappers resting with one knee on the floor and holding a Knife spear as support, even though they don't use knife spears or have any on them upon death.
If summoned using commands, ghost people will only be hostile to the Courier and their companions, and only the Courier's companions will be hostile to them. Other NPCs, however, will still say lines such as "Watch out!"