Watcher

Watchmen (Russian: Страж), previously Watchers, are a mutated species of large mammal. They are bigger and generally stronger than an average human or humanimal, have a dark tail, and are covered with dark-grey fur.

Overview
Watchers seem to resemble canines, both in behaviour and appearance. The watcher can commonly be found standing up on two hind legs sniffing the air or baying into the distance. A watcher's mouth is angled upward and sunken into the face, giving it a face reminiscent of a bull dog or boxer breed of dog. A pair of phalanges adjoin either side of the mouth and have some teeth lining the lower edge. These are probably used to give the watcher a greater surface area when biting, or to amplify its howls.

Watchers are pack hunters. The novel dictates that watchers will stalk their prey, observing them for weaknesses or a proper time to strike. When on the prowl, watchers usually move in packs from five to ten. In an exception to this rule, it's not uncommon to see hordes of 50 or more, as seen in "Tower" and "Echoes". Unless in these massive packs, they are almost never seen in open areas such as empty plains, because they're a potential food source of demons. It's unknown if they are hunted by slimeslugs. However, watchers also fear these creatures. Watchers have no preference as to what time of day they hunt and are found active at all hours a day.

Watchmen in Metro: Last Light has only altered cosmetically since their last iteration. With an overall heavier design, they seem to have undergone rapid but wholly logical changes in response to the nuclear spring. Of note now, is their more distinct variations in colour - now ranging several brighter shades of grey to browns that reach into oranges. These more pronounced colours act in part as camouflage, making them more difficult to see against the browns and greens of the surface. Watchmen in Last Light are also notable as being not wholly savage animals, fully capable of letting Artyom leave their home unharmed should he not fire upon them, remaining docile around Artyom when faced with sharing shelter from the storm, and even working cooperatively with Artyom to attack a common foe.

The watchmen in Metro Exodus seem to have a more chiroptera (bat-like) appearance, as seen with the elongated ear and teeth. Their claws even seem to support hand webbing, a common feature among the chiroptera. This suggests that either the watchers are heavily evolved and mutated beyond recognition under the conditions of the apocalyptic world, or the true origin species of watchers are actually bats. Along with their appearance is the fact that the redesigned watchmen's eyes are mobile, akin to chameleons. On the other hand, packs of watchmen can be seen/heard howling and growling exactly like canines do, which further supports their canine origin thesis. It's possible that watchmen in Moscow and other regions have came through via convergent evolution, and are not closely related despite their similarities in behaviour.

Mutated from
Watchers are the remnants of some undiscerned mammalian animal; likely descendants of rats, dogs, or even wolves (Exact taxonomy is unknown, however, due to the significance of mutation upon the watcher's behaviour and appearance). Their behaviour resembles such animals, they hunt in packs, they howl, they actively hunt as opposed to scavenging. Further evidence of a canine ancestry lies in The Gospel According to Artyom, where a pack of mutated dogs depicted as Watchers attack an young Artyom.

Habitat
Watchers are some of the most common mutants living on the surface. They are often seen scouring the city for food and have been reported traveling into the metro if food is available. Although it's unknown where they den, or any of their reproductive habits for that manner, watchers likely rest or conceal themselves in abandoned buildings, refuse piles, or vegetation; seeing as demons tend to pick off any caught off-guard in the open. They seem to be defensive of their homes as shown at the Kremlin.

Diet
Watchers are highly active and very social predators that both hunt and scavenge for any food available. The novel discerns that watchers tend to stalk their prey as they hunt them, observing them for weaknesses, and waiting for a proper time to strike. When on the prowl, watchmen usually move in packs from five to ten. In contrast to this average, it's possible to see hordes of 50 or more Watchmen moving about the surface in search of food. Watchmen also appear to be highly opportunistic predators, as they immediately move in to subdue and feed, when Artyom is fighting the bear; only having attempted to bring it and its cubs down earlier.

Appearances
Watchers are found on, or at the threshold of the surface. In Metro 2033, they are encountered by Artyom in Dead City 1 and 2, "Prologue", "Alley", and "Tower". In Metro: Last Light, watchers replace nosalises as most commonly encountered mutant type; being found in "Ashes", "Echoes", "Regina", "Sundown", "Nightfall", "The Crossing", "Bridge", "The Dead City", "Red Square", and "The Garden". In Metro Exodus, they appear in Moscow and around the Volga.

Tactics
The watcher, just like lurkers and nosalises, band together in packs of three to seven at a time and try to surround Artyom. This can be rather problematic, as they are met early in the both games, and can prove quick and sizeable foes. Even in Metro 2033, where ammunition is hard to come by early, any form of shotgun can be effective against them, as long as Artyom keeps his aim steady at the head or upper body. This method is encouraged in Last Light also, due to the attack patterns and habit of watchmen to charge at Artyom with their front body as a large target. Try not to miss too much because both Ashot and Duplet demand accuracy due to their small ammo capacity.

When they are howling, Artyom can take advantage of their instinct and score an easy head or chest shot - marking an almost guaranteed kill. This method is risky for constant use, however, as if he waits too long he will miss their chance, and other watchers will not have to howl to attack. It should also be noted that some will not howl at all, they will just attack without provocation or warning.

Watchmen also seem to be one of the more social mutants as they are almost always seen in a group. Their social behaviour also seems to extend to other species to a certain extent as they are shown to form temporary pacts when faced with certain situations. The Möbius trailer shows them working together with nosalises and lurkers to attack a station. They will also form these pacts with humans as shown by Artyom's encounter with the bear.

In the novel
Watchers are not mentioned by name in the book, but are encountered by Artyom during his trek along the surface from Polis to Smolenskaya. They are again described as having dark grey fur and stand on their hind legs before attacking or when watching their prey. They move in packs slowly and silently stalking Artyom from some distance in the cover of buildings, before getting closer and fanning out in a semi-circle shape to flank him. In the novel, they are the prey of demons who swoop down and grab any watcher not under adequate protection, which is why they stalk Artyom from buildings.

Trivia

 * Unlike the lurkers, nosalises, amoebae, demons, and librarians, you will not get an achievement for killing a certain number of watchers in Metro 2033.
 * There is only one quick-time encounter with a watcher throughout Metro 2033/Redux. In "Dead City 1", there is a watcher that feigns death. If Artyom moves close enough to it, the watcher will lunge and pin him to the ground. The player must then press the action button multiple times to make Artyom stab it in the neck or bash it with his knife. This is entirely avoidable by simply killing it before entering the building.
 * A new snow-covered version is seen in Metro 2033 Redux, and the Metro 2033 model for lurkers have been reused as watchmen babies.
 * Watchers had four eyes in Metro 2033, but in Metro: Last Light and Redux, this is changed to two eyes. The same is true of lurkers.
 * Although never mentioned, there is a possibility of watchmen being omnivorous predators, seeing as they are not the only apex predators in the Moscow food-web. It's also confirmed that they actively hunt for prey. This might mean that the watchmen are medium to high tier predators.
 * The Metro Exodus design for the watchmen bears a strong resemblance to the depiction of Barghest in the Dungeons & Dragons pen and paper RPG; an intelligent, evil creature with the body of a monstrous black wolf and a goblin-like face, based on the shapeshifting ghost of the same name from Northern English folklore.