Lore: Vilekin
The term vilekin is used to refer to a wide variety of creatures, constructs, and other entities. It is roughly synonymous with "monster," but also covers things like golems, monstrous humanoid-like beings (such as illithids and rakshasas), oozes, and plants. They run the gamut from tiny bug-like creatures that are mere nuisances to small populations, to enormous creatures that are capable of leveling all but the largest and best-defended of settlements.
During the Age of Empires - the time period in which the Arkeyan Empire, Jovian Compact, and Kiltian Republic rose to prominence and were at the height of their power - it is believed that significant effort was put towards purging the world of these monstrosities. Each of these three civilizations left behind evidence of great works and research specifically working towards vilekin eradication. Records suggest that there are many types of vilekin that were almost completely wiped out by these efforts.
While much effort was devoted to destroying the menace posed by these creatures, there was a smaller - but still substantial - amount of work directed towards understanding what caused these creatures and how to predict their movements. It was eventually discovered that myrrh trees acted as a sort of beacon for these creatures, and that specific types of vilekin were attracted to different forms of mox (such as chuuls specifically being attracted to amethyst mox). Even more distressing was the discovery that, the longer a given myrrh tree stood, the stronger the effect was - and the stronger the vilekin attracted by it.
Unfortunately, while they were attraced to myrrh, vilekin were not bound to stay near the trees that seemed to call them: as such, even at the greatest height of their era, the Age of Empires was constantly plagued by these creatures, leading to much of the world remaining wild and untamed. As their development of the Forces increased, this only made the world more dangerous, as vilekin would erupt into what were believed to be well-defended and safe locations, sometimes deep in the territory of the one of the three empires.
For reasons unknown, after the Fracture, vilekin activity diminished considerably. Some attribute this to what is believed to be a slowing of the growth rates of myrrh trees, which many find to be a dubious claim given the rarity of the trees to begin with (their growth rates therefore being difficult to study in a sensible empirical fashion) and a rather fragmentary record regarding their behavior from before the Fracture. Some believe that the empires of the day managed to cause a sufficient disruption to their populations that the remainder went dormant: while reports of vilekin attacks can be found in every era, post-Fracture they diminished almost the point of being mythological. Some supposed that, somehow, the vilekin menace had been dealt with permanently, and that no new vilekin would ever be encountered again, with those few reports being results of ancient creatures that simply refused to go into torpor.
Regardless, all of these hypotheses were laid to rest after the Omega Event. Within a few years' time, reports of vilekin sightings and attacks increased at an astonishing rate: while at first many of these creatures went unrecognized, it took the work of many memeticists sifting through the akashic record to determine what, exactly, they were seeing. Unfortunately, due to the geographical shifts induced by the Omega Event, many of the defenses and fortifications built in the intervening ages became largely useless against the new threats: and while advances in the Forces meant that many had the means to fend off these creatures, not all settlements in the world were so lucky. As such, a significant portion of the world has once more succumbed to trackless wilderness, populated only by terrible monstrosities. While airships and similar means of transportation mean that, for the most part, trade and communication were not terribly disrupted, this has significantly reduced the amount of overland travel and transit in comparison to prior to the Omega Event.
Worse yet, it has been found that some of these monstrosities are capable of surviving in the vacuum of space: while some thought to find solace from the creatures by running to one of the moons or further out in the system, it was found that some vilekin latched themselves onto these craft, or simply flew into the atmosphere and out into space under their own power. The vilekin, it seems, are far more versatile than any remaining records from the Age of Empires had possibly suggested.
It is important to note that while some vilekin can be communicated with - such as illithids, or rakshasas - they are classified as vilekin and not spoken due to their natures: these entities, and those like them, are anathema to other life in ways that are integral to their existence. Illithids, for instance, subsist on the brains of sentients, and are unable to survive off of other means of sustenance. Despite their capability for speech, the very nature of their existence is incompatible with that of spoken races. In these instances, it is this fundamental, irreconcilable incompatibility with spoken peoples that results in the illithids being classified as vilekin, rather than as spoken.
Other creatures, like chuuls, are incapable of communication and are clearly aggressive to other creatures, including spoken. In these cases, they are classified as vilekin - rather than just another clade of animal - because of two factors: first, they are drawn to mox and myrrh, which is not a quality seen in animal life; and second, they are usually possessed of incredibly more dangerous abilities than most animals. While a bear might maul you with its claws, and a boar might gore you with its tusks, vilekin instead assault your mind with weird psionic abilities, or twist time in ways that are simply unrecognizable. That most seem to also have a tendency to be intrinsically hostile to most spoken races is, for most, just confirmation of their suspicions that these creatures are not compatible with rational life in any way.