Trolls
There exists a fungal growth known to sages as athervospora tenebris, or simply the Dark Mold. Most fungi consume, the Dark Mold remembers. Nobody knows where it originated, but many speculate about the world's deep forgotten places. It learned to shape bones, it built muscles, it learned to walk, and then it had to learn how to feed.
A troll is not a creature in the traditional sense. It is a colony organism, "flesh" made of dense mycelial matter that are rubbery and tough, "bones" that are crystallized chitin structures secreted by specialized hyphae, and a "brain" consisting of a network of fungal nodes in the chest and head. There is no central organ that can be destroyed to kill it. Consciousness is spread throughout the entire mass, and this is why a severed troll hand continues to grasp and claw.
When a troll is wounded, the fungal network immediately begins weaving new tissue at remarkable speed. This is not healing, but is the same process by which the troll originally built itself. The re-attachement of severed limbs is particularly horrifying to witness. The separated pieces grow toward each other, extending pale filaments that interweave and fuse. A troll severed at the waist becomes, briefly, two creatures, each crawling toward the other with single-minded purpose.
This is why fire and acid are the only reliable means of destruction. Both destroy the troll at a cellular level, preventing the chemical signaling that allows reconstruction. A troll burned to ash has lost the memory of its own form, but a troll merely cut to pieces retains that memory in every fragment.
When a troll has fed well, it still attacks with the same relentless ferocity, but it no longer devours its kills. Instead, the troll tears chunks from its own body (a process that causes it no apparent distress) and forces this tissue into the wounds and orifices of its victim. It works the rubbery "flesh" into the victim's mouth, into the chest cavity, into any opening it can find or create. This fungal mass will immediately begin to spread through dead tissue.
This is why troll populations can explode so rapidly when left unchecked. A single troll in a populous area does not simply hunt, it converts every victim into a new colony. Every corpse left unburned is a seed waiting to sprout. Experienced troll hunters know to burn the bodies of anyone killed by these creatures, even if the troll itself escapes. A troll that flees a fight after making a kill is not retreating, it has finished.
The most disturbing accounts come from settlements that discovered troll infestation too late. Survivors describe finding missing villagers in root cellars and abandoned buildings, bodies swollen and splitting, new limbs already beginning to twitch. In one infamous case, a farming community lost to trolls was later found to contain seventeen nascent creatures in various stages of emergence, all seeded from a single parent over the course of one autumn.
A troll that has successfully seeded a corpse will often become more aggressive, not less. Ranging further from its lair, attacking more frequently, seeking new victims to convert. It is not satisfied, but instead is encouraged. The chemical memory of successful reproduction spurs it to repeat the process, again and again, until fire or acid can finally end its campaign. Some sages theorize that in regions where trolls have been present for centuries, virtually every specimen may be descended in a strange fungal lineage from a single ancient progenitor. The implications are unsettling: that all trolls, everywhere, may share a distributed chemical memory stretching back to the first time the Dark Mold learned to walk.
There are reports of trolls that have learned to avoid specific settlements, and trolls that seem to recognize individuals who have fought them before. Trolls sometimes display something resembling spite, returning again and again to attack those who have injured them. Is this consciousness, or a nascent development of memory?
Perhaps it does not matter. The troll that tears you apart will not pause to contemplate its own existence. It will simply feed, and repair, and endure, as it has for countless years, as it will for countless more.
The Dark Mold remembers. The Dark Mold hungers. And in the darkest places of the world, it builds itself new bodies with which to hunt.