If the Shellbrood are chaos incarnate, the Hiveguard are their polar opposites...but life doesn't exist on a linear continuum, it moves in cycles and spirals, fractally growing in all sorts of directions. Shellbrood seem to exist purely to destroy the world and remake it in an image that exists as a grotesque parody of its former self, they create nightmares and phantasmic dreamscapes that just aren't quite right, sitting somewhere between organic debauchery and rusted mechanistic decay. If anything, the Hiveguard are probably most similar to the 'Modrons' in Planescape.
The Hiveguard repair, restore and cleanse. Scholars tend to believe that they are the original caretakers of the Darkhive, eternally tasked with maintaining the structural integrity of the hive, as well as arcane and esoteric functions that have not been fully understood. They are no less dangerous than the Shellbrood, but for different reasons. Most parts of the hive are dirty and derelict, there simply aren't enough Hiveguard to maintain all areas at all times. Instead the Hiveguard swarm across the hive like locusts, sweeping away refuse and anything they are not programmed to expect in an area... Such unexpected encounters include Shellbrood, ships that have crashed into the outer layers of the hive, and most settlements. The Hiveguard are generally single minded in their job to restore the hive to its original state, but it is possible to reprogram them and many technomystics have become specialists in this feat (the problem is that this reprogramming need to be regularly updated as new mystic "software" sweeps across the hive restoring the "Hiveguard OS" in much the same way that the Hiveguard restore the Hive.
Many of the larger settlements have a small Hiveguard retinue, constantly monitored by a cabal of two or three technomystics (at least one of whom may be a 'Hooded Mystic') and a half dozen or more apprentices, such Hiveguard (and their watchers) are never fully trusted, because the 'Guard could turn at any time, reforming the hive and destroying anything deemed anomalous. Some of the smaller settlements and barricade slums across the hive deliberately keep their homes only slightly modified from the original hive, but deliberately throw rubbish a short distance away to act as a decoy when Hiveguard swarms approach (they tend to deal with the most anomalous areas first when they sweep through an area). Hiveguard seem to have six groups, which scholars refer to as echelons.
Skitterling - The Skitterling echelon is made up of tiny buglike swarms. The individual creatures are roughly an inch long and look like glistening black cockroaches or beetles, they are relatively harmless creature that squirt mild acidic cleaning sprays, using this with their tiny appendages to rip apart matter (organic and inorganic) into tiny chunks that are deposited in small piles around the hive. The problem is that they don't operate alone, Skitterlings are typically deployed in dozens or hundreds (and occasionally thousands), such groups can strip a cell of the hive in under an hour, obliterating anything that might once have lived there. Skitterlings are also capable of rebuilding a cell, but this usually requires overseeing from a member of a higher echelon.
Screecher - The Screecher echelon is made up of packs of metallic crablike creatures, different coloured sheens on their shells indicating different duties. Screechers derive their name from the screeching sound their claws make a ross the hard surfaces of the hive floor. Black Screechers seem to control a few dozen Skitterlings, Green Screechers roam the corridors along common patterns, Red Screechers clean up the piles left by Skitterlings, Gold Screechers repair other Screechers and Skitterlings, Purple Screechers erect temporary force fields while other Hiveguard work in a cell, Silver Screechers act as defense against any who might seek to do damage to the swarm.
Duplicant - Duplicants look like spidery assemblages of spare parts from all the other Echelons. Using these parts they construct Skitterlings (takes a second or two), Screechers (takes a minute or two) and Nodes (takes around an hour). Whenever they encounter fallen Hiveguard, they add the components to their mass, until new Hiveguard need to be spawned. Duplicants are the most common Hiveguard for Technomystics to seek control of.
Node - Nodes resemble hovering balls of glowing plasma, at the centre of which can be seen a vaguely dragonfly shaped construct. Nodes move very slowly, and emit a hum both physical and psychic. This hum gets louder when there are fewer Hiveguard around, making some scholars believe that it functions as a homing beacon for the mechanical community. Scholars have also noted that the plasma spheres surrounding nodes pulse in erratic rhythms as Hiveguard are regularly reprogrammed, suggesting that this Hiveguard echelon function as communication hubs for the community.
Biofactory - There are said to be 12 Hiveguard biofactories, each one at the center of one of the pentagonal cells around the hive. None have seen one of the Biofactories directly, but their existence in intuited by the fact that fragments from Skitterling piles are typically transferred to these locations, while completed hive parts are transferred back out of these locations where Duplicants and Screechers connect them back into the hive structure. It is suspected by some scholars that the so called "Biofactories" are simply a part of the hive itself.
Intellect - Striding the corridors of the Hive in vaguely humanoid forms, the few Hiveguard known as the Intellects are rarely seen and rightly feared when they do appear. There have never been more than three of these beings recorded at any one time, and more often a lone Intellect roams the ancient transitways. In the presence of an Intellect, the hive itself can act erratically; doors sealed for generations might spontaneously open (others might close), lights may activate (or deactivate), ancient relics may spontaneously erupt into power (or shut down), and portals may spontaneously connect different parts of the hive. As long as it is respected and left in peace, an Intellect will continue on its path, a few rare stories of Intellects being hindered or attacked typically end with the absolute devastation of entire villages, thought it is suspected that many other vanished settlements across the hive have met their demise at the hands of a Hiveguard Intellect, there were simply no survivors left to tell the tale.
A few rarer types of Hiveguard have appeared, but they aren't common enough to be included among the regular echelons.
Black Guard - In areas where the Hiveguard have regular contact with the survivors of the hive, sometimes a humanoid Guard takes form. These robotic entities have basic communication skills, operating as diplomats between the survivors and the hive. Black Guards often work closely with cabals of Technomystics, but rarely last more than a few weeks before they wander back off into the hive, or break down into component parts before reforming as screechers and duplicants.
Phaseling - These ghostly Hiveguard don't seem to fully exist in the same reality as the rest of the hive. They appear like giant spidery forms, often as the centre of energy webs in abandoned hive cells. Phaselings seem to create temporary portals that allow Hiveguard to rapidly traverse the hive in ways that survivors haven't managed to decipher (psychic travellers have some ideas how this might work). Beyond transport duties, Phaselings are occasionally seen engaged in other activities, but it is a mystery to what ends these may lead.
(Note that from a worldbuilding perspective, there are a lot of hooks deliberately left open with regard to the Hiveguard...there are just as many open elements for the Shellbrood, allowing GMs and players to shape elements to their story needs)
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