Of all the creatures in the Rusthaven sourcebook, one of my favourites is the Murkstones. They come in two variants, the common Crawlers and their much rarer creators, the Builders. Created by the Iron Wind, these strange creatures are part living stone, part machine, part creature. While many think of them as two separate creatures, they are actually the same thing, just different parts of the life cycle.
Murkstones start off as Builders, huge, hulking chunks of rock with a mass of segmented tentacles underneath them. Most die before they can get airborne, but a few make it into the sky by ablating their outer stone to form Crawlers. These crawlers can be thought of like extra limbs for the Builder, and they spread a thick mucus all around the Builder which through a manner unknown, allows the huge stone creature to generate lift and hover into the air. Once airborne, Builders become far more dangerous as they can now make proper use of their tentacles. Immediately, you’ll notice on a Builder that two tentacles are different to the others. At first, they gently feel their way through the mucus patches, as if looking for something. It is not until the other tentacles start their work that they can be satisfied.
Using its main cluster of tentacles, the Builders emit high-energy beams into the mucus that burn and transform the slimy substance into hard lines of shiny metal. As soon as these lines form, the more delicate tentacles latch on and the behaviour of the Builder rapidly changes. Using its Crawlers, it begins expanding the area of mucus it calls its territory, etching more complex and larger designs into the mucus, all connected together. As the complexity of the design increases, so to does the Builders actions and motivations, almost as if it somehow making itself smarter with every etching. The strange lines, reminiscent of those found inside many numenera, have a secondary function however. As their complexity grows, they seem to draw down the wrath of the sky itself, causing lightning storms, and each bolt that hits the etchings is absorbed into the design and draw up by the Builder for its own mysterious purposes.
My the time a Builder has spread its domain to a few square tens of miles, it has reached its most dangerous form. Intelligent, deadly, the Builders act with a complexity of thought and planning that can not be understood. The Crawlers under their thrall take on an increasingly disturbing agency all of their own - quite a departure from the dumb crawling rock-beasts they begin their lives as. However, apart from the storms, people seem to have little to fear of Murkstones other than getting in their way. Murkstones seem interested in only one thing - killing others of their kind. The Builders seem to guard their growing intellects jealously and will not tolerate the existence of others. They hunt down and eliminate any others they find, and wars between Murkstones can be a terrifying thing to behold. They never reuse the etched territories of their victims, instead sending their crawlers to destroy them utterly and rebuild new mucus over the top for its own expansion.
With all this talk of intelligence, one might wonder how you can even tell they think at all? Those few people with the ability to commune with the numenera of the ancients can hear its growing thoughts as they reach out into the mindscape of machines. At first, a Builder thinks as an animal, but as it develops soon it surpasses the thoughts of even a the most erudite nano until soon its mind as as incomprehensible to us as ours are to the insects under our boots. What they think of in that state, no-one knows, but rarely does a Murkstone stick around for long - a blessing many would say. At the height of their power, they seem to just disappear, winking out of existence, the Builder and its Crawlers both. Where they go, the Aeon priests can only speculate, but many think it may be a higher realm of the mind, where flesh and form are no longer welcome, perhaps the datasphere, or somewhere else entirely.