Trolls are supposed to have developed out of humans ("no two trolls are alike, as no two humans are"), but are barely recognizable as such due to their distorted features and multiple, disfigured limbs. They do not grow much bigger than a human, short of changing into a giant.
The presence of a troll always brings a clear and present risk of getting (non-immune) humans infected with the Illness, but unlike with other monsters, the distance over which infection can take place ; more specifically, the "wheezing" ones exude their infectious breath up to one meter around themselves, and the "spitters" can cover ten meters. The mechanisms through which the Illness turns a fraction of its victims into monsters, in turn, remain unknown so far.
Physical Disfiguration Edit
A major reason for the statement that "no two trolls are alike" is that humans develop extreme, highly individual bodily deformations as they turn into trolls, while beasts largely preserve the semblance of their former species.
The end result may well vary from fast-running hunters to massive ambushers, as shown by the two trolls in "spot 24". Among the rather common traits are growing extra limbs, ribs acting as limbs, and extending the spine into additional body length or a tail.
Mental Capacities Edit
It is possible that the human might regain a certain level of consciousness and speech, because humans that became part of a giant provably can when the giant is killed or dismembered. As a whole, however, their typical characteristic is that they will approach and attack humans and human settlements whenever they notice any - however, see the special case of Vættur below.
There are contradictory hints on the intelligence that trolls (and giants) have. On one hand, they seem to be kept out of safe areas by rather simple means (palisades) and do not get wise to the ever-identical tactics of cleansers. On the other hand, they are repeatedly said to not start an attack indiscriminately, suggesting that they do have the capability of weighing their options beforehand.
Fighting Trolls Edit
Trolls are vulnerable to fire, and Cleansers start controlled fires to destroy their nests. Sunlight and moonlight seems to either incapacitate or discourage them.
They are also sensitive to low temperatures, retreating into a "nest" which they also use to lie in ambush and wait for victims. The nest Sigrun locates on is a dark place hidden deep within the building, overgrown with "meat moss" and dripping wet - which supposedly are characteristic features for such nests.
She also gives out orders on which suggest that, while a gunshot is bound to attract the attention of nearby monsters, killing one with a knife blade - thus giving it time to attack the human(s) as well - does not. Hence, communication between them must be rather poor.
As established on , vættur are a subtype of troll that avoid attacking (humans, at least) and rather stay in hiding, observing and learning the habits of those passing by. It is believed that this behaviour serves later attacks that lead to people gone missing without any hints left of what happened. Pre-Rash Finland had the dedicated term of "metsänpeitto" for similar incidents caused by maahinen.
Note that while the terms "troll" and "vættir" were in existence pre-Rash, they had an entirely different meaning, to the point that trolls were a subcategory of vættir, instead of the other way around. Also, regional differences between and historic changes of the meanings make it all but impossible to authoritatively translate even the pre-Rash term "vættir" to English. Its original cognate was "wight", but translators have been meandering through "wight", "gnome", "goblin", "imp", "fay", "boggart" etc. ad nauseam in attempts to provide an appropriate match.
Another subtype of troll that usually refrains from attacking humans are the (literally "water revenant"), trolls inhabiting bodies of water well protected from weather extremes, mainly "sheltered bays and coves along the Norwegian coast". The working theory is that these trolls were somehow got caught in such waters, and adapted accordingly, resulting in bloated bodies, usually very passive behaviour, sometimes sessile to the point of immobility.
However, once a sjødraug has been disturbed by humans to the point of attacking and managed to make its way onto dry land, its grown mass and thickened hide make it rather difficult to kill it and the physical power that allows it to move in the first place also make it dangerous opponent.
When dealing with one, Sigrun notes that the best tactic for killing trolls of this size and strength is to walk away slowly, luring to troll away from water and beaching itself so that it would die from dehydration or sunlight.
Duskling EditDusklings are a form of troll first appearing on , though Lalli claims to know them from earlier, and contributes the name. Dusklings, having what seems to be a shell of soil and plants covering their back, are partially protected from sunlight, allowing them to venture out at dawn while the sun is still out. Dusklings speak in a childish manner, in incomplete sentences or even isolated words. They greet and address their prey - which means, pretty much anyone besides their own kind - as "food". While weak by themselves and not possessing much strength or protection, a whole horde of Dusklings poses a substantial threat to humans.
- While en route to Mora, Tuuri saw the burned-out husk of a troll hanging on an electric fence. Emil said such sightings are rare.
- A vision of a troll (dubbed "Hippo Shrimp" by fans) appeared to Lalli just before the attack on the Dalahästen.
- The creature Emil sees in the shadows of a building as they enter Kastrup, nicknamed "Ol' Dangly-Eye", is quite likely to be a (live) troll as well.
- In the makeshift hospital that is "spot 24", after the team noticed a Vættur in the vents and started to search for monsters, Sigrun finds a troll nest. In the room preceding the nest, a dead (not-quite-yet?-)troll, codenamed "Ceiling-Face" by the fandom, is still stuck in the restraints of the gurney he had been put on.
- Later on, Emil finds himself in battle with two trolls, "Tooth Scary" and "Wallhugger", requiring extraction by Sigrun to escape the latter.
- Towards the end of chapter eight, the cat-tank awakens the particularly flat "Leaftroll" as it drives through an unstable building with a mostly-dead nest. Leaftroll later attacks Reynir, and Sigrun and Mikkel kill it.
- In chapter ten, fleeing the Kastellet(?) ghosts in the cat-tank while the sun sets, the team awakens a number of grosslings. The Jelly Long Legs are confirmed to be (just) trolls, while "Rootroll" is likely the sjødraug subtype.