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, this is essentially their world. It's probably no coincidence that playing this game always gives off the feeling of being watched by something, because you most likely are.
The majority of mutants are species that have high reproductive rates, a prime example being the many 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.
- Dark Ones - Very powerful species of sentient humanoids with telepathic abilities that attempt to communicate to the player. They are the results of mutations in humans, and are also known as "Homo Novus".
- 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.
- Lurker - Small, numerous, and agile creatures likely mutated from rats or small dogs.
- Watcher - Large mutants covered with dark grey fur, and known for their distinct howling.
- Demon - A giant bat-like creature found only on the surface.
- Spiderbug - Large, scorpion-like insects that are deathly vulnerable to light.
- Shrimp - Large chitinous marine mutants found in the underground metro "river" and the swamps on the surface.
- Librarian - Quasi-intelligent beasts, very dangerous. Found only in the library. There are 2 varieties: common and black. Their appearance resembles grotesque gorillas; passively suggesting they are mutated from humans or apes.
- Giant Amoeba - A large explosive ball of protoplasm, which seeks out living creatures and explodes on contact.
- Biomass - A very large mass of radioactive organic material found on top of the D6 reactor, acts as a boss-like creature for the player.
- Nosalis Rhino - A massive nosalis leader that acts as an alpha female to common nosalises.
- Bear - A bear that was affected by the radiation, now a powerful boss-entity.
- Slimeslug - A mutant only mentioned, even in the book. Slimeslugs are very powerful presumably predatory snail-like creature that leaves slimy trails in its wake.
- Mutant Crow - Mutant crows are small bird-like animals living on the surface and have the ability to fly.
- Corpse Eaters - Corpse Eaters are non-lethal scavenger mutants that feed on the corpses of all creatures including members of their own species.
- Newcomers - Large black bony mutants only ever mentioned in the first book while Artyom is at Paveletskaya.
- Liana - Large tentacles that hang from the ceilings of the interiors of buildings.
- 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 the player.
- Ghosts - Though not true mutants, ghosts are strange afterimages of people/creatures that died in the metro and have not passed on.
- Darkness - Ill-defined patches of ghost-related darkness that renders electric light useless.
- Damned Souls - Malevolent dead that cannot move on, and drag down anyone they are able to reach.
- Anomaly - These supernatural bright, blue balls of light will electrify and kill everything around them as they drift through the metro.
- Great Door - A seemingly hypnotic entity found in the lost catacombs, embodied by a large red door.
- River of Fate - An anomalous flow of water, said to be able to change the destiny of those who enter it.
- Nagornaya Phantoms - Giant supernatural entities obscured by fog who kill the youngest member of groups to apparently consume their life force.
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 in 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.
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.
- 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; rat hordes are known to roam the tunnels.
- Bats - Slightly hair-less 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.
- Pigs - These livestock have 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.
- 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.
- Chicken - Also brought down into the tunnels; chickens are raised in fewer stations but are nonetheless a commodity. Like pigs, they're raised upon mushrooms and are noted for being slightly more emaciated looking than chickens grown on different diets.
- 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 Hole Station before it was attacked. A dog named Karatsyupa also appears in accompaniment to 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.
- 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.
- 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.
- 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.