Leshen Ecology

In-Game Information
"Dwelling deep inside the forest, these creatures use their innate magic to control all flora and fauna within their territory."

-Monster Field Guide, Monster Hunter: World

Taxonomy
The Leshen does not and never belonged to any biosphere of the known world, hailing from another world different than even Behemoth's, the monster cannot be categorized conventionally.

While the Hunter's Guild seemingly unable to put the creature into pre-existing classification, the witcher's guild from the world they came from does have their own system of classification in which Leshen is considered a Relict, a group of creatures and beings with no real uniformal trait beside shared weakness towards a special type of blade oil made by witchers. This category is somehow adapted by the Research Comission into their compendium.

Habitat Range
Like Behemoth before it, Leshen is an invasive species of world-to-world scale, either voluntarily or not. This is true even in the world where the creature and witcher Geralt came from as their species were transported there through a cosmic anomaly known as "Conjunction of the Spheres". In all known premises however, Leshen seems to favor biomes flourishing with life, particularly those with healthy, living trees and other floral growths, in which the Leshen will try to establish its role as the habitat's "Guardian". For said reason, the  Ancient Forest of the New Wolrd was an obvious choice for the creature to set in.

Ecological Niche
Leshen easily dominates over lesser life beings, especially those weak of mind. Its ability to take control of other lifeforms such as Jagras and Revolture and even tree roots easily gives it dominance towards creatures that are vulnerable towards its control, and significant power it can use against those who are immune. Leshens has been shown to be able to  dispatch weaker Wyverns like Pukei-Pukei in its effort to attack the Chief Botanist. Its capacity to face more powerful monsters remains untested, persumably because the Leshen had no reason to do so, as it usually remains hidden when no scritiny towards the forest is being done.

Biological Adaptation
The Leshen's appearance and ability in the perspective of Known World's understading would be the high point of being "inexplicable". People on the creature's previous homeworld even came to see Leshen as more of an spirit than a flesh and blood creature. It is not understood exactly how much common ground Leshen have with mundance creature (metabolism, respiration, reproduction etc) if any at all, beside the fact that they can be dispatched with enough damage inflicted upon them, just like any monster.

The creature's body is dominantly composed of wood-like substance that is molded into an eerie and tall humanoid form with long, clawed arms and a head of animal skull complete with a pair of antlers; the form might seem impractical for combat, but this matters little since Leshen rely heavily on teleportation and manipulation of other lifeforms in combat, unlike most creatures in the Known World who primes their physical combat prowess.

Barring its magic, the Leshen is neither fast or agile, and its sole advantage in physical combat are its razor sharp claws that can cause heavy bleeding upon heavily armored opponents. The creature is also quite durable despite its appearance, but this, as indicated by Geralt of Rivia, might be the result of the Leshen absorbing nutrients from the Known World, which made it stronger than its average brethern from the world it came from, the theory is further supported by Geralt's statement's as he examines stray bones in the New World which he finds to be very strong, and concludes that "everything here (New World) seems to be well-fed".

Leshen's magical ability is the creature's true trump card, along with its cunning. Leshen's magical ability can be roughly divided between its manipulation of lifeforms and teleportations. Leshen's manipulative ability allows it to command lesser lifeform to its will and uses differently: Leshen would use Jagras as attack hounds to distract and incapacitate opponents. Revoltures are used for quicker attacks on further distance in a form of a wave, or as a living shield with them flying around the Leshen in high speed. Tree Roots usually function as means to strangle opponents or delivering heavy and wide-reaching blows, these roots will burst from the ground with such force that is enough to hurt a smaller wyvern severly, or throw a human into the air.

Leshen can teleport, as or "immaterializing" into black smoke and reappear elsewhere in the vicinity, usually already hallfway into executing the next attack move. This ability easily compensates its lack of natural agility and makes its slow movement to be dangerously deceptive; The Leshen could appear distances away in different direction to to launch unexpecting wave of Revoltures or suddenly appear behind its opponent to sink its claws in.

The Leshen also have several vulnerabilities. Leshens are very vulnerable towards fire, especially those of magical sources like the Igni Sign or the Flame Manipulation. Such flamses can easily set the creature ablaze in panic, though not for long. In the world it came from, it is neccesary for witchers to use silver weapons against Leshens so they can effectively inflict damage which normal steel weapons couldn't do, this is done because the creature counts among magical monsters supposedly vulnerable to silver. This law does not apply in the known world however, as the weapons forged in Astera, either through sheer physical power or nature alien to the Leshen's biology, could work nicely against the Relict despite not having silver forged into them.

Behaviour
Leshens, unlike mundane mosnters seems to show not only a curious degree of thinking capacity, but also a potential spark of higher reasoning. Leshens seems to develop affinity with the forest it inhabits and will actively protect it, not only when intruders are physically threathening the Leshen, but even small scrutiny that wouldn't have harm the creature in any immideate way. Some belive the Leshen does this out of an inherrent intent to protect the forest while others belive it is simply territorial behaviour on high-maintenance. Some occurences, like how Leshen could appear picky on who it decides as target, or how it made a pack of Revoltures kill an Aptonoth for no apparent reason adds to the confusion to understanding Leshen's motives.

One aspect remains clear: Leshen will not cover trails of its pressence in a habitat and would even build marking totems to signify its territory. Tresspassing these perimeters does not warrant immidieate attack, but destroying them is the ultimate invitation for a fight towards a Leshen who would immidieatly arrive to annihilate such offender. Witchers often use these method to challenge the Leshens they're hunting for a duel to the death, Leshens would likewise reciprocate with the utmost aggresion.

It is unknown what a Leshen do beside guarding the forest it resides and ocassionaly fighting off offender, thus little else about the creature is known.