The Body

The Body is a large void that composes most of the dimension of Reeval

Background
Given that the plane is at the very least the size of an entire galaxy, if not larger, and that the rest of the Thread making up the Body often act like a single mind, the Thread could be considered the largest single living creature in all existence, in any dimension. Even if isn't, it would still be enormous to worlds with little to distinguish from one part to another. The only variance provided would be the few voids that lie within kits depths like bubbles within a white sea, plus the occasional infestation or disease.

Creatures that find themselves pulled into the Body without a source of breathable air are soon after smothered. In addition, the constant pressure of the writhing, wormlike strands of the Thread will inflict 1 point of damage every minute of exposure to creatures that don't have any rigid armor or some other form of protective shelter. But this anathemic environment isn't directed, Rather, the Body, for all its interest and resultant "Nibovian" probes into alternate dimensions, is ill-equipped to sense individual creatures that invade it purposefully or accidentally. The Thread creates voids to act as interfaces with entities it sensed inside of alternate dimensions. If someone truly wished to avoid the Thread's attention while still residing within Reeval, they might best be served by exiting the voids, where Thread Walkers as the eyes and ears of the Thread.

Exic Infestations
Some regions of the Body will contain hollows that aren't created by the Thread, but instead by the voracious appetites of verdant, spider-like creatures called exics. The exics are a species of transdimensional vermin that lucked out a few centuries prior and discovered the Body. Ever since then, the infestation has eaten out dozens of cavities inside the Body, ranging from the size of a cavern system to an entire planet. These cavities are somewhat like the voids, except not purposely created from the Thread. Still, though, most will have breathable air and gravity about them. The cavities are crisscrossed with greenish exic webbing, hives, and crawling swarms of exic. Though the infestations are immense and growing, the Thread occupies an unimaginably greater volume, which might be part of the reason as to why they haven't noticed said infestation yet. For their part, the exics quickly trap any Thread walkers that would appear inside the infested Zones and ,for that matter, any explorer venturing throughout the Body.

Diseased Regions
Regions of the Body suffer from various illnesses, and sometimes even die. Dead regions contain a mass of blackened, non-illuminated and non-moving strands. As horrible as the writhing wormlike community is to most explorers from the base dimension, these lightless, rotting, necrotic sections of Reeval might be even worse. Diseased regions usually won't last long, however, as healthy strands would eat and displace the dead and dying strands. But one diseased region will owe its demise to an extraterrestrial object that radiates lethal, invisible energy. The object in particular acts like a toxic thorn in the Body's flesh, killing off a wider and wider swath of Thread each year. Unlike the exic infestations, though, the Thread are aware of this region, and have sent various sub-unit Thread walkers to assess the situation. The object is a cast-off stellar remnant that had somehow transported interdimensionally to Reeval.