Nightkin

The nightkin were an elite warrior caste in the Master's super mutant army and the apex of his creation of super mutants. When the Master's super mutant army was defeated in 2162, many began wandering the wasteland or banded together into groups of varying sizes and with varying ends. In 2281, many are now either with Tabitha, Marcus or Davison, with the last group desperately searching for more Stealth Boys to feed their addictions to it.

Fallout
Nightkin can be found in the upper levels of the Cathedral, as well as inside the Mariposa Military Base, and in random patrol encounters in the cells around the base. After the Master's fall, many surviving Unity super mutants had become a chaotic wasteland-wandering force, set on destroying everything it encountered. They are superior to other super mutants in skill, equipment, and weaponry. Many of the nightkin are equipped with cloaking devices, such as Stealth Boys. The only gaming effect of this is to give them a slightly ethereal look, as it does not affect the player character's chance of hitting them.

Fallout: New Vegas
Some of the nightkin appear in the Mojave Wasteland, very often suffering from severe psychological damage, caused by prolonged Stealth Boy use. They wear the same clothes as regular super mutants, but many of them also wear hoods and stop signs strapped to their forearms as makeshift shields. They are often found wielding rebar clubs, miniguns, incinerators, super sledges or, in the case of nightkin masters, bumper swords. They are slightly more articulate in their speech and are believed to be a stronger and more intelligent version of first-generation super mutants, according to Black Mountain Radio. They are weaker than standard super mutants, however, as a result of their use of Stealth Boys. There are some scattered in the wasteland, in places such as Black Rock cave.

The nightkin under the banner of Tabitha harbor an "isolationist" ideology, openly warning humans to stay away from Black Mountain, and even commenting on the dangers of "the dreaded battle cattle" and "two-headed bear people," a reference to the animal mascots on the flags of Caesar's Legion and the New California Republic, respectively. A nightkin camping on the outskirts of Novac kills one of Dusty McBride's brahmin every night around midnight. He can be found during the day, cloaked behind a boulder across the road and to the west of town. Here, he can be heard complaining about his constant insomnia and trying to silence noises in his head that he believes come from the brahmin. Despite their phobia, some nightkin have become Antlerists, and take orders from their god, Antler, an inanimate brahmin skull located in the basement of the REPCONN test site.

The companion, Lily, is a nightkin and a former soldier in the Master's army.

Nightkin play an important part in the quest Come Fly With Me. The Courier is sent by Jason Bright, the founder of the Bright Brotherhood, to take care of "demons" that are infesting the basement level of the REPCONN rocket testing facility.

Similar to the super mutants in Fallout 3, nightkin will attack ghouls.

At Brooks tumbleweed ranch a nightkin will appear next to the Courier and start a chat. He will offer to sell them wind-brahmin for all their caps. If the offer is declined, he will turn hostile and proceed to attack. Originally, if the Courier accepts the offer without asking about the price, no caps will be removed, and the nightkin will give a free Stealth Boy instead. Another Stealth Boy will be in his inventory available for pick-pocketing. However, with the game patch as of July 7–8, 2011, the nightkin will no longer give a Stealth Boy upon agreeing without question and will take all caps. The nightkin will only have one Stealth Boy that can be pickpocketed or looted from his body.

Another nightkin, Dog and his "human" personality God, appears in the add-on Dead Money. Although he does not use Stealth Boys, he is still a formidable fighter. Notable nightkin include:


 * Tabitha, supreme commander of the State of Utobitha.
 * Davison, leader of a rogue group of nightkin who attacked REPCONN test site and the Bright Brotherhood, and is the focal point of Come Fly With Me.
 * Keene, leader of the Jacobstown nightkin looking for a cure for their condition.
 * Lily Bowen, a former assassin working as a herder in the mountain refuge.
 * Dog and God, a split personality nightkin and key to Elijah's plans.
 * Chupacabra nightkin, a rogue mutant attacking Dusty McBride's brahmin.
 * Brooks tumbleweed ranch nightkin, selling wind brahmin (tumbleweeds).
 * Black Rock cave nightkin, with seemingly precognitive powers.

Fallout: Brotherhood of Steel
After the death of the Master, parts of the super mutant army gathered and formed a new faction, led by Attis. Many years after their regrouping, these mutants captured the Secret Vault in order to use the FEV reserves stored inside. Attis' goal was to continue the Master's plan. His army had an elite unit of nightkin, much improved in skill, and equipped with high-tech stealth suits to enhance their abilities. These suits served the same function as Stealth Boys. These suits probably originated from or were made in the Secret Vault.

Biology
The nightkin share all of these characteristics with their brothers. They differ in that they are the perfect fulfillment of the mutation, with the highest level of strength, resiliency, and their intelligence retained or even enhanced by the process. Subsequent alterations to their biology were caused by prolonged use of Stealth Boy technology. The stealth field caused permanent recoloration of their skin pigment, to a gray-blue color. More importantly, it has caused neuro-chemical changes to occur in their brains, leading to mental instability and disorders, including schizophrenia, delusions, and even split personalities.

Their superiority resulted in the development of an arrogant, borderline chauvinist personality in many nightkin, not helped by the preferential treatment they received. As nightkin developed their mental disorders, however, their personality slowly changed. They slowly started to lose tolerance for being seen, relying increasingly on their Stealth Boy to remain invisible to the naked eye, fueling a vicious cycle of cumulative mental damage. 

Appearances
The nightkin appear in Fallout in the Cathedral and the Mariposa Military Base, in Fallout 2 as a hostile encounter on the world map, in the Secret Vault in Fallout: Brotherhood of Steel, and make a comeback in Fallout: New Vegas and the add-on Dead Money.

Behind the scenes

 * In Fallout: Brotherhood of Steel, the nightkin are voiced by Michael Bell.
 * In Fallout 3, the word "nightkin" occasionally appears in the password list when hacking a terminal.
 * The mutant commando advanced character class from Fallout Pen and Paper d20 was based on the nightkin role in the Master's Army.
 * Nightkin have an obsession with the brahmin, manifesting as worshiping a skull (Davison), killing them to stop their mooing (the Chupacabra), and one nightkin attempting to sell "wind brahmin" (tumbleweeds) near a tumbleweed ranch.
 * Joshua Sawyer conceived of the nightkin becoming schizophrenic from Stealth Boys and was directly inspired by the novel The Invisible Man and his progression into insanity by taking an invisibility drug.

Bugs

 * In the original Fallout, some nightkin that fight unarmed disappear (become "invisible") during the player's turn in combat and can not be targeted. The only way to end a battle with them is to either flee the area or have them be killed by an accidental fire, e.g. by other enemies that miss and hit them or using a burst mode of a weapon targeting any other available target with the intent to hit the supposed "invisible" nightkin.
 * In Fallout: New Vegas, the shaders that make nightkin invisible are sometimes bugged, causing them to remain invisible after deactivating their Stealth Boys (although they will be treated as visible for the purpose of calculating V.A.T.S. percentages). This has been observed in the REPCONN test site basement and during the encounter near McBride house in Novac, and appears to be linked to reloading a previous save during, or immediately after, an encounter with a nightkin (possibly after being killed).
 * After the nightkin that has been attacking Dusty McBride's cattle is killed, a nightkin master can appear near the tent in the middle of Novac; it can be encountered as far away as the Highway 95 Viper's encampment, and rarely can even spawn inside the McBrides' house. This nightkin master will be neutral unless attacked by the player character but could be encountered fighting Vipers. If killed, this nightkin will have a minigun in very poor condition and possess The Screams of Brahmin note.