Personal record, Dr. Brian Virgil. This will likely be my last recording.
My requests to shut down the FEV program have repeatedly been denied. We've learned nothing useful in the last 10 years. I have to take matters into my own hands. What we're doing... it's not right. It needs to stop. If anyone should find this after... after I'm gone... know that I never wanted to hurt anyone. Anyone! Do you understand me? I'm going to make sure the whole program is shut down. If not for good, then at least for years to come. After that...I know what I'm about to do will be seen as a betrayal. Treason, he'll probably call it. So... I'm leaving. I have a plan... and if it works, I'll be somewhere safe. Somewhere not even the Coursers can find me. Everything that we've done, the lives we've taken... if there is a god, may he have mercy on us all.
The Institute's strain of super mutant is unrelated to the West Coast and Vault 87 breeds, but they do share many similar traits such as caging prey, bagging body parts, and feeling superior to humankind. In the terminal entry 0769-CM22 aboard the Prydwen, it states that the Commonwealth mutants are not related to those from the Capital Wasteland.
The super mutants encountered within the Commonwealth are in fact the unfortunate victims of failed FEV experiments, created and disposed of by the Institute. In August of 2178, the Institute relaunched its FEV program under the direction of a man named Dr. Frederick, presumably with stored samples from the pre-war experiment that created Swan. The FEV research lab was then constructed in the back of the Bioscience Division wing and a team of researchers began experimenting with different strains of the FEV virus. Two years after they started their experiments, in the year 2180, a horde of super mutants attacked Diamond City, but were repelled by the newly formed group known as the Commonwealth Minutemen.
To supply the program with test subjects, the Institute abducted wastelanders from all over the Commonwealth to experiment on. These subjects were examined, logged, then submerged directly into FEV. If they survived the process they were subjected to multiple experiments and cognitive tests. Once finished, some were discarded back to the Commonwealth, creating the scourge of mutants currently present in the year 2287. This method of trial and error was used to perfect different strains of the FEV, with the overall goal of improving the synthetic organics program. In March of 2224, the synthetic organics research team had come to an impasse. They had perfected two promising strains of FEV, however these weren't adequate enough to progress their research due to their test subjects being exposed to an excessive amount of radiation. The team decided to explore new avenues of exploration in order to advance research, however the Directorate decided to continue the FEV program in hopes of learning more about the FEV's potential.
The program was last under the direction of Dr. Brian Virgil and his deceased predecessor Dr. Syverson. Virgil decided he could no longer live with himself knowing that he was ruining the lives of so many innocent people. He states that they have learned nothing new within the past ten years, back to the events of Fallout 3. Virgil destroyed the research lab and all of the research, which is logged as "Incident V" in terminal entries. He then proceeded to transform himself into a super mutant using a unique strain of FEV to flee into the Glowing Sea. The FEV program was finally ended after over one hundred years of abduction and experimentation.
"You humans made us - now suffer for your arrogance!"
”— Super Mutant battle cry
Their mouths are depicted as being closed much like Marcus, unlike the Vault 87 super mutants which carry a permanent snarl. Furthermore, in regards to previous appearances, specifically the Vault 87 super mutants, these super mutants have a darker skin tone and appear more scrawny and with less pronounced muscles.
The existence of the behemoths suggests a link with the Vault 87 strain of FEV, as they are the only super mutants known to continue growing with age. However, the green-brown coloration is closer to that of Mariposa strain of FEV, specifically resembling the super mutants seen in Fallout: New Vegas.
Unlike their brethren from the Capital Wasteland, the Commonwealth mutants possess a relatively advanced understanding of armor, weapons, and at least some minor knowledge of craftsmanship in comparison to their brethren. They appear to trade stronger physiques for the knowledge to utilize/create weapon and armor mods, and even have access to reprogrammed security systems such as searchlights and automated turrets not unlike their far-western cousins. This is presumably the result of advanced experiments within the Institute.
Higher rank super mutants show more intelligence than their brethren, speaking more eloquently, and utilizing some advanced tactics such as cover, shifting position and taking high ground; compared to their lesser brothers who will often ignore cover and simply try to get as close to an enemy as possible, even when armed with long range weaponry.
Both Institute and Vault 87 mutants appear to share the ability to be somewhat educated due to the existence of mutants such as Fawkes and Uncle Leo from Fallout 3 and Strong and Erickson in Fallout 4.
Like their Vault 87 brethren, a number of the Commonwealth super mutants seem to want to preserve their new species, since they can be overheard speaking about "green stuff" in some areas (such as Trinity Tower). This appears to be a hole in lore, as mutants in the Commonwealth are likely made over the years by the failed FEV experiments of the Institute. Given this, it is difficult to gauge how mutants are so widespread—implying hundreds, if not thousands of Institute captives—and no actual appearance of FEV outside the Institute exists, unlike in Fallout 3.
Super mutants can randomly be encountered around the Commonwealth in small groups, usually raiding parties, which can attack player character made settlements. Much larger groups can be found infesting various buildings throughout the wastes. They have developed a unique relationship with mutant hounds, and will utilize these beastly creatures as attack dogs, usually encountered in groups of 1-3. Mutant hounds are unique to Fallout 4 super mutants, instead of the centaurs that have normally accompanied them in past installments of the game series.
The most common and weakest variety of super mutant. They carry a pipe weapon and drop minor and low-tech loot on death. They can usually be taken down with minimal effort. They can often be found among more powerful varieties of super mutant such as a skirmisher.
A super mutant that will run at the player character with a beeping mini nuke in its arm. It will then detonate itself while in close proximity, killing its enemy and itself in a fiery, nuclear explosion. Shooting the mini nuke in the suicider's hand or targeting the right arm in V.A.T.S. will cause the mutant to explode prematurely, killing it instantly. As a result, shooting the bomb from afar is one of the most effective ways to dispatch them, and potentially other nearby enemies as well. If one is desperate to kill a suicider and the only weapon types available are unarmed and/or melee, the player may either sneak attack it, or run up to it, strike it, step back a bit, and repeat until it's dead (though the latter is not advised as one missed attack will allow the suicider to detonate the mini nuke, and accidentally hitting the mini nuke with either type of attack will detonate it). The suicider can be detected before it is seen by listening for the beeping of its mini nuke. If the suicider is killed without detonating the payload, which can be done with a headshot or body shot, a mini nuke can be looted from its corpse, otherwise only nuclear material will be found on its remains.
Utilizing the Blitz perk, it is possible to kill the suicider in V.A.T.S. with a melee weapon before it explodes, even if it takes several hits.
Super mutant skirmishers are significantly tougher than regular super mutants, taking more damage and usually carrying more powerful weapons. Skirmishers will appear more frequently once the Sole Survivor reaches level 10.
A force to be reckoned with, super mutant masters have an extremely high hit point pool and superior damage resistance compared to their weaker brethren. They are generally equipped with heavy weapons such as the missile launcher or minigun. They can be generally found in locations with a large mutant concentration, an example being Big John's salvage.
The primus spawns at level 45+ and is seen with large groups of super mutants, most commonly at major super mutant outposts. They commonly wield super sledges or assault rifles, but may also be seen with missile launchers, and rarely, Fat Man launchers.
The third strongest super mutant, the warlord is very dangerous as he is much stronger than most of his brethren. Their extremely high hitpoints means that they can withstand multiple head or limb shots from extremely powerful weapons like Gauss rifles without being crippled.
Behemoths are the most powerful super mutants by far, towering above any player character, at about 20 feet tall. These super mutants are the oldest and strongest of their kind. As well as being many times larger than any other humanoid creature, almost as large as a mirelurk queen, unlike regular super mutants they will not speak - instead they will make monstrous roars. They are armed with a fire hydrant mounted on a large pipe; other than that, they have the ability to throw heavy boulders at their enemies. Either way, both weapons are heavy-hitters, and will cause major damage against any enemy smaller than them. They carry a cage made from shopping carts on their backs, similarly to their Vault 87 counterparts, which they use to carry boulders that they use during combat.
Epic behemoths are an immensely powerful variation of average super mutant behemoths, and, to some extent, are more clever in combat. They tend to appear in forest areas, which they may use to their advantage by hiding behind trees. They also will block their face with their hand quite often, especially when fighting at melee range, allowing for a chance to get in several hits. They are more upright than many standard behemoths in appearance, and although they are quicker, they use similar fighting techniques, such as smashing, knocking the player character down and hurling boulders. Aside from being able to sustain more damage, they can be crippled if low on health, and will slump to the ground on their side, where they can be finished off.
These behemoths are the toughest and oldest mutants found in the Commonwealth. They are most likely some of the first FEV experiments that the Institute conducted and have grown over the decades into ancient behemoths.
If the Sole Survivor manages to shoot a suicider's mini nuke while hidden, it will not affect the detection status, even when the suicider explodes in direct sight of other mutants. They may or may not start to investigate the body for a short period of time.
The mini nukes that super mutant suiciders carry seem much larger than the standard mini nuke, appearing more similar to the Mark 28 nuclear bombs used by Liberty Prime and found inside the Sentinel site.
The Sole Survivor can find a semi-educated super mutant named Strong at the top of Trinity Tower. He can be recruited as a companion after completing the quest Curtain Call. Unlike super mutant companions from previous games, Strong is far from civilized, often stating his desire for mutants to kill all humans and mentions wanting "someone to eat" when hungry.
The noise of a suicider's mini nuke is comprised of two parts, a continuous beeping and a tone. This tone is a Shepard tone illusion, wherein the tone sounds like it is continually rising in pitch, but in reality it is not and is just a loop.
Super mutants have been heard wishing to hunt humans not only for food, but for sport, in contrast to their Vault 87 brethren which have only been seen to hunt for food and FEV fodder. While they occasionally kidnap settlers for a ransom of caps, this is likely a fault of radiant quest placement as they don't appear to have any need for conventional human currency, unlike raiders.
Super mutants refer to the Brotherhood of Steel members as metalheads, as they can sometimes be heard saying "Wish metalhead was here so I could smash him".