Mutants

Mutants are organisms whose DNA has been altered by radiation, or as a result of being exposed to various chemicals. Mutants appear both in the novels and in the games. They are usually fierce and dangerous creatures, not hesitating to attack or kill any human that crosses their path, although certain exceptions exist, with mutants that are generally neutral, or even intelligent beings who try to communicate with humans.

Overview
Mutants of a common variety are generally tough creatures, which have adapted to their nuclear environment and can withstand high levels of physical trauma. Derivative from local fauna, the mutants of the surface world and the Metro often display above normal intelligence and, as a result, most species will travel and hunt in packs. While their behavior and movements are rather similar from encounter to encounter, scripted scenes keep gameplay fresh and exciting. Most mutants of the Metro are beings shaped and evolved to life in darkness, as this is essentially their world.

The majority of mutants are species that have high reproductive rates, a prime example being the numerous lurkers. This could explain that in a mere 20 years, almost all surviving species with high reproductive rates are completely mutated from the radiation.

Below is a list of all the noteworthy mutant species in the Metro. More information on each can be found on their respective page.

Animal mutants

 * Bat - A mutated, aggressive version of bat that living in Vladivostok.
 * Bear - A bear that was affected by the radiation and grew to monstrous proportions, now a powerful boss-entity.
 * Biomass - A very large mass of radioactive organic material found on top of the D6 reactor, acts as a boss-like creature.
 * Blind Ones - Giant gorilla-like mutants living in the abandoned research facility at Novosibirsk. They might be a family of the librarians or a related species.
 * Błotniak - Semi-intelligent, humanoid, mutated creatures living in the Vistula, but also capable of breathing and movement on land. Somewhat similar to the mythical Slavic utopiec/topielec (drowner) creatures.
 * Corpse Eaters - Corpse Eaters are non-lethal scavenger mutants that feed on the corpses of all creatures, including members of their own species.
 * Dark Ones - Very powerful species of sentient humanoids with telepathic abilities that attempt to communicate with Artyom. They are the results of (possibly deliberately engineered) mutations in humans, and are also known as "Homo Novus".
 * Demon - A giant bat-like creature found only on the surface.
 * Giant Amoeba - A large explosive ball of protoplasm, which seeks out living creatures and explodes on contact.
 * Humanimal - A humanoid mutant severely affected by decades of radiation, both in appearance and behavior. These once-humans have not only abandoned civilization, but have regressed to an animalistic state, and will attack their human cousins on sight.
 * Librarian - Quasi-intelligent beasts, very dangerous. Found only in the library. There are two varieties: common and black. Their appearance resembles grotesque gorillas; passively suggesting they are mutated from humans or apes.
 * Lurker - Small, numerous, and agile creatures likely mutated from large rodents.
 * Mutant Crow - Mutant crows are small bird-like animals living on the surface and have the ability to fly.
 * Newcomers - Large, black, bony mutants only ever mentioned in the first book while Artyom is at Paveletskaya. The same mutants are described in more detail in Metro 2034, though this time they are described as being large, pale, and having no eyes. They're also extremely durable and blindingly fast. It's possible that these are different mutants that chased out the original "newcomers".
 * Nosalis - A common mutant found in the metro that likely mutated from moles. There are six varieties in Metro 2033: common, black, winged, albino, plated, and rhino.
 * Nosalis Rhino - A massive nosalis leader that acts as an alpha female to common nosalises.
 * Shrimp - Large chitinous marine mutants found in the underground metro "river" and the swamps on the surface.
 * Slimeslug - A mutant only ever mentioned, even in the books. Slimeslugs are very powerful, presumably predatory snail-like creature that leaves slimy trails in their wake.
 * Snakes - Though largely unchanged by radiation, some of these reptiles have developed bug-like legs and pincers on their tails.
 * Spiderbug - Large scorpion and spider-like arthropods that are deathly vulnerable to light.
 * Tsar Fish - A large aquatic mutant inhabiting the Volga river.
 * Upyirs - Medium-sized mutants mentioned in Metro 2034. These mutants are named after vampires due to their likeness to large bats, though they are not demons as they crawl. They have small leathery looking wing folds under their arms, as well as webbed hands and feet. They are known to attack entire stations in waves.
 * Watcher - Large mutants covered with dark grey fur, and known for their distinct howling.
 * Wolf - A pack animal that has remained virtually unchanged by radiation.
 * Worm - Giant leeches living in a flooded station of the Novosibirsk Metro.
 * Reaper - A creature more than three meters tall, with a long, woolly, dark pole on its body and tail. Its front limbs are one and a half times longer than its body, and end in long sickle-shaped claws (which is how it got its nickname). Has a keen sense of hearing. Isn't very fast while running, but can leap across obstacles in quick bursts.
 * The Swallow- Resembles a long gray caterpillar. The body is similarly elongated, with the front of the body curving upward at right angles. At the very top of the curve is the mouth. The swallow's body is also covered with hair. Six furry spider-like legs stick out from under the swallow's belly, with which it can move quickly and silently, or walk sideways like a crab. Each such paw ends in three predatory curved claws.
 * Nops - Heavily mutated and altered dogs that are almost entirely changed by radiation.

Plant mutants

 * Liana - Large tentacles that hang from the ceilings of the interiors of buildings.
 * Nettle - Inside the terminal and under the port in the Volga area are bushes containing poison gas. Both locations suggest some chemical or biological research, which may or may not have been related to their origin.
 * Radioactive Luminescent Mushrooms - Common throughout the metro, these mushrooms either cause or feed off radiation.
 * Spore Bud - Inactive plant species that poses no harm to Artyom.

Supernatural phenomenon

 * Anomaly - These supernatural, bright blue balls of light will electrify and kill everything around them as they drift through the metro.
 * Damned Souls - Malevolent dead that cannot move on, and drag down anyone they are able to reach.
 * Darkness - Ill-defined patches of ghost-related darkness that renders electric light useless.
 * Ghosts - Though not true mutants, ghosts are strange after-images of people/creatures that died in the metro and have not passed on.
 * Great Door - A seemingly hypnotic entity found in the lost catacombs, embodied by a large red door.
 * Nagornaya Phantoms - Giant supernatural entities obscured by fog who kill the youngest member of groups to apparently consume their life force. It is, however, possible that these are not supernatural beings, but mutants who've somehow gained the ability to create fog.
 * River of Fate - An anomalous flow of water, said to be able to change the destiny of those who enter it.
 * Master of the Tunnels-A disembodied entity and a revered character of folklore, the keeper of the St. Petersburg Metro.

Other mutants
In the novel, a few other mutant species are mentioned in brief, these include wild dogs and a giant bird stuck in an even larger cobweb at the library. In Metro: Last Light, fishes displayed at markets have a powerful muscular pair of pectoral fins which resemble limbs; many fish, however, look reasonably unmutated.

Other creatures
Numerous other non-mutated animals and plants are also mentioned to have survived throughout the Metro. Several of these creatures can be sighted also on the surface; as well as many different types of plants blooming in the area.
 * Bats - Slightly hairless versions of the common variety in Moscow have taken to the Metro and fly about its tunnels. They can be seen both in and on the outside of the Metro tunnels; feasting on insects and scavenging corpses. Bats are also known to fly both in and out of the metro at will; leaving its pipes to brave the winter.
 * Cats - Although very few are seen, two men in Polyanka own one when Artyom passes through. Reasonable doubt though arises as Artyom suspects the men and the cat may be ghosts, but Artyom finds it difficult to believe. Stray cats are also encountered by Artyom throughout the Metro; one being noted as having a quite intelligent expression and having bright green eyes.
 * Chicken - Also brought down into the tunnels, chickens are raised in fewer stations but are nonetheless a commodity. Like pigs, they are raised on mushrooms and are noted for being slightly more emaciated looking than chickens grown on different diets.
 * Cockroaches, Flies, Spiders, etc. - Cockroaches can be seen in the loading art for Metro 2033. Flies can be seen also when looking at a corpse in Metro: Last Light, flying onto Artyom's gas mask in some areas. Various ambient insects can be heard outside and others can be seen flying under lights.
 * Crows - Normal unmutated crows can be seen flying in the distance during the credits of Metro: Last Light. Despite the apparent crow-like creatures flying on the surface, these regular crows can be seen flying in small flocks. The major identification of these birds comes from the fact that crows shown during Artyom's flashback of his mother before the war are identical to the crows flying in the distance during the credits. The very sprites of the birds are the same during each instance; making it more than likely they had survived the Great War of 2013.
 * Deer - Living in the wilds of Poland and Russia, these hoofed mammals have survived with little to no mutation and remain mostly harmless to humans.
 * Dogs - Dogs are believed to be prevalent all throughout the Metro system; in the company of man of course. Many can be heard in crowded stations (and quite a few serve as guard dogs); most notably at Hole Station before it was attacked. A dog named Karatsyupa also appears in accompaniment to the Revolutionaries when Artyom encounters them. Artyom also assisted in finding a small puppy who lost its way in the Metro. Slightly more mutated dogs are also said to live on the surface; Artyom being "witness" to an attack by them. It's ironic how little is seen or mentioned of these dogs in the games, considering Moscow and its Metro are notably host to a very large population of street dogs. However, Metro Exodus does show several instances of dogs (noticably german sheperds) and their trainers/owners, indicating a large population of this breed was saved from nuclear annihilation.
 * Frog - A small amphibian largely unaffected by radiation.
 * Hare - A small mammal largely unaffected by radiation.
 * Pigs - This livestock has become a staple of the Metro-dwellers diet. Raised in almost every station; pork has become a dietary staple and precious commodity being its one of the few animals humans have brought down with them into the Metro. These pigs themselves are raised on farmed mushrooms and, despite living in obviously poor conditions, have grown quite large and seemingly healthy.
 * Rats - Mostly unmutated Brown Rats that scurry about the metro scavenging refuse, fungi, insects, and meat from corpses. There are many variations to this common rat; the closer you are to the surface the more visible mutations there are among the rats. Large rotisserie rats can also be seen being served in Venice. Also, rat hordes are known to roam the tunnels.
 * Seagull - In the games they are seen only in the Sam's Story DLC of Metro Exodus. These medium-sized marine birds have remained practically unchanged since 2013.

Other plants

 * Mushrooms - The inhabitants of the Metro also known for making due with a limited number of crop types. Agaricus bisporus, known as the common mushroom, portobello mushroom, or champignon mushroom is grown in bulk under the low light conditions and is a staple crop for the Metro inhabitants. Mushrooms provide the basis for several types of alcohol such as beer and Shroom Vodka; although Mushroom Tea is also a known product. Yeast is also known to be cultivated in these low light tunnels.
 * Plant Crops - Food plants are also available to Metro-dwellers, of which, moss is the most common and readily available. Potatoes and Tomatoes are still known to be cultivated by people. These plants, however, are particularly hard to come by and are known to be grown in underground hydroponic farms. It can also be assumed that in addition to these; drug plants are also grown such as Marijuana and Tobacco. Both of these products are known to be in use by Metro citizens, but Marijuana in particular still has a negative perception as taboo. Several ambiguous plants can also be seen in Metro: Last Light growing under special light in designated areas.

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