Servitors

There are ten grades of servitors. The manifestation of the higher grade servitors happens when the nodes grow large enough, strenghtening the influence of the dark lords over the surrounding area. It's a rough comparison, but the lower level servitors are about comparable to appropriate steps (for as long as you compare them to combat classes.   Grade ones = First Step. Grade two = Second Step. Grade three - Third Step. Grade Four - Fourth Step. Then things get more complicated, as while the Grade Five equals lower Fifth Step, Grade Six equals higher Fifth Step (so, about levels 125-150). It's hard to say how it works above that level, as nowadays those levels basically do not appear.   The servitors are also divided roughly between the seven types, concerning the general role they play on the battlefield. Those types are as follows:
  Commanders - All-rounders without extreme strength on any field, but with comparatively high intellect. This means that they tend to be the smartest of the servitors, capable of figuring out some advanced strategems. It's an unofficial rule that each time a network expands enough to manifest first higher grade servitor, they will be a Commander (precisely to avoid doing something stupid and ruining the whole thing).
  Casters - Artillery or 'magic users' of the servitors. High damage, but typically fragile. To off-set said fragility, they tend to be the second ones after Commanders when it comes to intelligence level. You can also expect them to be very, very good at crowd control. In a variety of ways.
  Swarms - Typically the absolute cannonfodder, not even considered a 'regular' part of any servitor army. Low-intellect, high numbers, akin to animals although still to a degree driven by the hivemind behind the Network they belong to. The name comes from the fact that they tend to try to swarm any sapient they come across, with extremely limited application of tactics.   Grunts - Exactly what it says on the tin. Dedicated melee-fighters that form the bulk of any servitor army. Vary from goblin-sized humanoids to entities resembling giants (especially on higher Grades). Unlike Swarms, they are capable of using at least some basic tactics in any skirmish, even without a Commander around. Still relatively common and - perhaps due to that - often underestimated.   Champions - Encountered typically on the higher grades. You can expect them to be deadly on every distance and in numerous ways, and generally be close to the worst things to be encountered out there. The threat of their manifestation grows steadily the closer you get to spawning the higher grade one. It's less than 5% for the second (for example) 4th Rank in the Network, but 95% for the tenth 4th Rank.
  Deviants - Servitors who do not fit into the other types, very often crafted for a single specific purpose. Sometimes they might even lack a patron, and instead be working' for more than one Dark Lord at once. A good example are the dreaded Cancer Knights, created by the Dark Lords as a counter to the human Immortals during the Great Multiversal War.

The servitors do not reproduce biologically. Instead, they are spawned by Servitor Nodes - a minuscule distortion in the fabric of Reality that allows unprocessed raw mana of the Dark Lords to exist.   This only happens away from System's attention, so in places with minimal or no presence of the Sapients or Spirits. Affinity overflows, even the weakest ones, render themselves immune to the presence of servitors.   With large swathes of natural ecosystem being at least partially overflowed with particular affinities, it's not easy for larger servitor presence to pop up anywhere without anyone noticing it.   Once that happens, Servitor Nodes begin to spawn servitors, both to defend themselves and to grow stronger.

Servitor Nodes are actually forms of a spatial distortion that is capable of interfering with the System, allowing a larger amount of non-purified magical power to flow into the universe. As a result of that, servitors begin to spawn in the area, attempting to secure the bridgehead into reality.   Such a node begins a minuscule mook factory, producing weak servitors that will engage everything in sight. They'll also attempt to gather as much mana as possible, to pervert it back it into its original form, thus expanding the node. There are three levels of those, typically called 'Lesser/Medium/Greater Nodes'.   They always appear as a form of a floating crystal, varied in colours and shapes, buzzing quietly. The difference is in the quality of produced servitors. Level two produces Grade Two, level three produces Grade Three ones. Visually the biggest difference is in size: lesser ones are about twenty centimeters in diameter, medium ones are fifty centimeters in diameter, and greater ones are about meter in diameter.   The crucial term is 'about'. The varied shape means that they can look very differently, and almost never resemble any geometric form.

Servitor Lairs are formed when a node grows large enough to begin to warp an area of space around it. It's not yet strong enough to form a proper foldspace, but it gets there. The servitor lair is where the nodes begin to multiply, expanding their bridgehead with more and more nodes.   The result of that is a growth in the amount of dark lords' influence over the area, leading to the spawning of stronger servitors from the central node, typically Grade Fours. This is where things begin to actually dangerous, as sufficiently large lairs can deploy thousands of servitors to attempt to murder and destroy anything in the vicinity.   Lairs that actually form and survive more than a few weeks are those that formed in defensible positions. Ruined fortresses, caves and so on.

It's a rare event, but sometimes things just go very, very bad. When that happens, servitor lair grows strong enough to actively fold space around it, allowing it to continuously expand itself while allowing it to massively improve its own defensiveness.   Formation of a hive is often an apocalyptic event. Even the best case scenario is a large scale war, with servitor hives capable of producing entire armies of servitors every few months.   The only positive of their is that the folding of space limits their ability to grow by drawing in ambient magic from the background. This means that the hives will not grow on their own. This means that a hive can technically be kept in check, for as long as the hive is properly locked and it's unable to harvest more magical materials to facilitate its own growth.   An example of that is the Ruin-53's Murdered Coast, a past of the Aurian continent that was devastated during the Great Multiversal War due to it being a servitor stronghold.   This place is continuously spawning Grade Six servitors (and a lot of Grade Five), however their attempts to march out of the coast are continuously thwarted by the defenders of the nearby mountain range.

You can generally expect them to pop up pretty much everywhere. However, singular First Grade servitors are an easy prey for most humans, meaning that in the civilized lands (or inhabited, even) they are promptly disposed of. Making them the local equivalent of JRPG's slimes or western RPG's giant rats and similar creatures. The problem starts when they managed to gather up and establish a lair - or anything above that.   You can expect them to start becoming a menace when they start overtaking some mostly undeveloped or abandoned areas. Eventually, if nothing is done, they can take over an entire region - and when they do so, then dislodging them from their fortified holdings will be extremely hard.

Greatly varied. You can expect Caster and Commander-types to be intelligent pretty much on the level of humans (if not more). Swarms-types will typically lack any degree of creativity and sapience, and are pretty much animals guided by the species-wide instinct. Grunts, Champions and Deviants vary on the field.   However, even the smartest servitor is driven wholy by the will and intellect of their Dark Lord. There is no such case as a non-hostile servitor - they will attempt to murder any human (save for those worshipping the Dark Lords) in sight, regardless of how 'civilized' they appear. Their 'settlements' appear unnatural, as expected from what's pretty much a hivemind.   Their 'intelligence', in short, isn't given to them to create a society. It is given to them to execute the orders of the Dark Lords in a more creative way, to be able to improvise ripostes to the actions of the humans. They are not sapient.