The real question: where shall these roots dig to retrieve nutrients? Also, is this the primary method of feeding?

Naturally, the entity doesn't require nutrients or any biological-based nourishment. Their body is completely inorganic, which means that they'll have to "feed" themselves with inorganic material as well over time, depending on how much inorganic matter their cell imitations require to replicate themselves or replace tissue - which also means that their body is constantly mutating, evolving, and enhancing upon itself. This however is a very slow and unnoticeable process as most of it happens on atomic levels.
If their body doesn't lose matter through unnatural causes, they will not need any additional matter. Maintenance though is still a requirement should particles within them break or cells cease. This replacement and feeding procedure can happen with these hand and foot tendrils. They give the entity direct contact with the environment and can transfer the elements to the analysis chamber directly. How "far" these tentacles travel in order to dig for useful materials is only limited to penetration, for example- they wouldn't be able to simply dig through a wall of stone, to keep it simple. Whether the absorbed material is useful or not will depend on the analysis itself.

It isn't "any" matter their body needs. You may view their inorganic manifestation as a table of pure element and chemical diversity. A diversity which is required to sustain environments of all kind. It is also related to their "abilities", how well elements within them transfer electric signals, and whatnot. This diversity is also the cause of radiation. Most elements are, in fact, highly radioactive and could potentially kill creatures on long exposure to their form. Not to mention that the "shimmer" (a non-solid, gaseous "cloud" surrounding the entity at all times, capable of solidifying into a network of veiny-looking tendrils) would also scramble up brains and tissue. This network does help the entity to scan the environment, though. Their feelers are already capable of measuring temperature, moisture, etc. - which is the case with any proboscis their form has - but the shimmer is like an enhancement.

But regarding the "roots", material absorption and 'probing' isn't the only functionality these have. It reaches into a more connective sense as well. To quite literally sense another one. And should the entity find it necessary, study them thoroughly, where this connectedness may lead to mental and physical control.
Attaching the roots to someone's body, letting additional, smaller growths run underneath the skin of someone else in order to connect to their neural stems, and so on. For the sake of science, I suppose. Though that isn't something the entity does on a daily basis.

Forgot to mention, whether it is the primary way to ingest materials or not all depends on the situation and environment. All proboscis and growths are useful for different tasks. A true primary method doesnt really exist.

Then surely you have mutated/can mutate other methods, such as a method to dig through a wall of stone. Imagine them being able to root into the ground of a metalyard and a gigantic, blue, mass glowing with "shimmer" grows right in the center. Reaching to the corners of the lot and eating whatever inorganic materials they can only continue to grow.

My next question is probably, where is the limit to their growth? Also, what sort of control do they have on people- as you mentioned the being connecting to the neural stem of a person. <3

Well, reaching through a wall of stone certainly sounds easier than it is. While the entity could "eat" themselves through stone, with the proboscis alone wouldn't be able to do that. It requires more tools, more complex networks of growths working together. But I suppose that the smaller the roots/growths are, the easier they can reach into potential air pockets within stone. This way, stone could be broken apart easily. Not to mention that the shimmer could pretty much do the same. Well, all of their body could de-solidify upon command in order to pierce or wander through surfaces. Some empires don't call them a "spirit" for no reason, randomly appearing in buildings, vanishing as quickly as they arrived.


The "limit" is where spare matter comes into place. It all depends on how much spare matter their form contains to create additional growths. Their manifestation contains "nodes" which are - in fact - highly condensed elements in the shape and colour of small, black pearls/spheres, similar to the "core" - though the core itself is larger and stored within a separate area. These nodes are usually stored within the "crystal cave" or other chambers within them. They are very heavy, some reaching tons of weight even. (I know, sounds a bit funny when you think of it) but the "weight" problem has become meaningless the moment the entity became powerful enough to upkeep a passive-anti-gravity field. (Nothing machine-related. It is all environmental.) The core has weights of unimaginable masses due to the element "Placentium", an element which can only be found during the birth of a universe, the "seed's shell", so to speak. The condensed element allows the entity to manipulate space and even time through gravity. Since we all know... basic science... the heavier an object, the more it will bend space. And together with additional abilities, Mirage can even "tear" through dimensions. A very risky procedure, generally avoided as it could annihilate existence.

Their organs aka. "bulbs" as I like to call them function both as long time storage for materials - and the breakdown of organic- as well as inorganic matter.
Additional growths generally don't require a lot of matter to create. If you want to view it on a more galactic scale, the unfolded matter within them could easily reach among the surface diameter of a giant supernovae. Possibly even larger, should the entity decide to consume more.

Regarding the control you speak of, there are a lot of ways how Mirage can control and manipulate people. It reaches from basic acts up to the mind-breaking.
But regarding the neural stem you mentioned, that is just one of many acts they can perform on inferior life forms. And even that manipulative method has a lot of diversity.
The easiest way would be direct control. Either by laying a hand on a weak spot of the "victim" where the stinging cell-covered growths can enter the skin, or by well - forcing growths into available openings. Usually oral as it is the closest to the brain. The goal of this act is to connect their own to the victim by spreading these roots thoroughly. That on the other hand alone can lead to various different outcomes. But yeah, I think you should get the general idea. Brain and nerve manipulation, so to speak. The victim will be nothing but a puppet on strings, quite literally.