Really, it's almost like you anticipated some of the questions I would have. However, I do want you to expand on a few things:
Its prey preference seems to be skewed towards large and vaguely humanoid entities, such as Skin-Stealers, but if it has not eaten for a considerable period of time, it will eat anything that is not a human or a humanoid entity.
My main problem is that I feel that everything past the word "anything" isn't needed. I think you could just replace that bit with the word "living". The wording here just makes it seem like it will stop searching for humanoid entities and focus on non-humanoid entities if it is extremely hungry.
Kills made immediately after major evolutions are typically characterized by seemingly random deep gashes across the corpse or an incomplete decapitation, all usually accompanied by severe arterial or venous damage.
You mention ahead of this that kills made a large amount of time after an evolution tend to be only partly consumed and make it seem that ones made right after a large evolution aren't really very damaged. However, this contrasts with the description of how much energy they need. If they needed a lot of meat, it would be more logical they would eat all of the prey they catch (perhaps excluding bones), meaning there wouldn't be a body to look at. One can already get an idea of the injuries one might abstain from the entity based on how it kills, so there really isn't a need to describe marks on bodies. At most, regarding the remains of meals, I would just say they leave fractured and splintered bones.
I was thoroughly impressed with the article, but then I stumbled upon this section that could benefit from some improvement:
For this reason, we'll tell you once, and only once, to stay the fuck away from this thing, we do not need this thing to start associating people with threats.
If Entity 142 starts killing people unprovoked, we won't be able to stop it, especially if it evolves to counter our weapons, so just save us the trouble and don't even think about getting close to it.
For your safety, and for ours.
The article has maintained a neutral tone so far, but this particular section seems to disrupt that neutrality. If you were issuing an official warning from M.E.G. to advise people to stay away from the entity, you would want to provide reasons and present the information in a formal manner. As for the log, it might be a good idea to include a content warning for gore at the beginning, just to be on the safe side.
Getting to the end of the log, you say that Nova got an Entity 19 infection. Was Entity 142 somehow responsible (Does your entity carry Entity 19)? Or was Nova infected by chance? Just wondering.
Honestly, other than that, I can't think of anything else to mention conceptional-wise. Moving on to the SPaG critique on Monday(just to let you know, that is going to take a bit longer than the conceptional since I include repetition under that and sometimes point out details that aren't necessary when doing SPaG).
SPaG:
I'm going to go line by line, point out the error, and explain it to you.
Currently, there has only been one recorded individual, though there is always a possibility that there are more, because if it were a species, different individuals would look the same due to the lack of known reproductive capabilities.
While this sentence is technically correct grammatically, too many long sentences can wear out the reader. Can you try breaking this up?
This may suggest that, if it were a species rather than an individual, it could clone itself, although it must be emphasized that this is a theory, and is not proven without doubt, therefore it is highly recommended to treat Entity 142 as one entity, and apply the same caution to any entities that look similar.
Since this is a new addition to your article, I'm going to ask a conceptional question and do a SPaG correction.
Conceptional Question: What suggests that this species could clone itself? I realize that in your article you didn't point out an reproductive abilites, but I didn't ask you about them(although I considered doing so) because it felt that if you left it out, readers wouldn't really care about the absence of such information. I feel this bit right here is where I would point out reasons for why you should have kept it as a species, but I'm going to hold back until we get through SPaG critique and perhaps another round of Conceptional Critique.
SPaG:
Try switching up your sentence types. This is an extremely long run-on sentence. Using too many compound, complex, and compound-commplex sentences, or too many of the same type in general, can sound like you are droning on and will bore the reader. Run-on sentences can be hard to understand and are so long that they do the same thing as having too many of the same sentence type throughout a paragraph.
As for humans, it will ignore them, but if it is provoked, the chances for survival are low
Meh. I would suggest rewording this. It's grammatically correct, but I think it would sound a lot better without so many commas. A comma signals a slight pause and there would be a lot of pauses in this one. Furthermore, you forgot to include a period at the of the sentence.
Entity 142 is also completely immune to neurological and physiological effects, such as the effects of the pastries on Level 67, or the radiation on Level 10.1.
Since there aren't more than two items in the list here, you can get rid of the comma before the word "or".
Currently, Entity 142 is a lean yet muscular humanoid standing at a height of approximately seven feet tall, with cyan skin, a spherical head which floats above its thorax, rectangular black eyes with white irises, and extremely large pupils, which are said to provide it with exceptional night vision.
While the comma before "which" isn't needed, you can stil keep it if you wish since it would still be grammatically correct with it. It would just get rid of a pause in the sentence that isn't needed.
Additionally, after Encounter Report 142-1, there is thought to be a large keratin layer underneath its skin that protects it from projectiles and explosives.
Nothing wrong with this sentence, I just think it would be best to define the word "keratin" in a footnote. This is because not everyone may feel like opening a tab and looking it up on google. It would be better to just have the information right there. I don't even know what it is.
Its ability to evolve gives it remarkable survivability, but it is also extremely taxing, and micro-adaptations are constant due to the ever-shifting nature of the Backrooms, therefore, it must eat titanic quantities of food to sustain its ceaseless evolution.
Another run-on sentence here. It would be best to break it up with a period between the word "Backrooms" and "therefore".
What is classified as a "major evolution" is unclear, but most theorists define a major evolution as any adaptation which significantly affects its bodily functions; for instance, on Level 7, it may adapt gills to help it breathe underwater, flexible muscle to help it swim faster, or stronger night-vision to see in the water.
Change "which" to "that". Since the information beyond "which" is essential to the sentence, you would instead use "that". Normally I wouldn't correct such a thing, since it would be a mistake not many would notice, but I just fel like it :).
During a major evolution, Entity 142 will construct a nest and enter a state of suspended animation, presumably in order to evolve in safety.
Please define "suspened animation" for the reader. Why would it enter a state of suspended animation?
The time it spends in suspended animation is unclear, but it is theorized that the time spent is proportional to the scale of the evolution in question.
Simply to avoid repetition, find a synonym of "theorized".
Researchers suggest that it does this to generate "checkpoints" so that it can quickly navigate towards "desirable" levels, namely, those with a high entity population, and it is thought that this is done to fuel its evolution.
The comma before "and" and after "population" is not needed since "and" is not the end of a list.
This drastically increases the time wanderers must spend locating a level exit, making it much more dangerous to even remain in the level they are in, especially levels with a high entity count, which makes it more likely that they will be killed, subjected to insanity, or subjected to passive level effects that are fatal.
While this isn't a run-on, it is extremely long. Please try rewording or breaking it up a bit. In addition, you need an "'s" attached to the end of "level" since the effects belong to the level.
Its voracious appetite is believed to be caused by its constant evolution and is also thought to be the primary motivator for its preference towards levels where entities are plentiful.
Mainly because you've mentioned this before (the place where you mentioned it is qouted below), you don't need this sentence.
"Immediately after, it will exhibit an increased appetite and begin hunting non-stop, attempting to eat as much as possible, presumably to replenish the energy lost from evolving."
Moreover, its general preference towards dangerous, large entities has caused it to develop immunity to biological, neurological or any other effect that other entities are capable of afflicting it with, such as a Scream Eater's emotional effects on nearby entities.
There is a comma needed after "neurological" since it is signifiying the end of a list.
Furthermore, since other entities can't afflict Entity 142 with any of the affects mentioned, you should change it to say it can't be affected by effects entities are normally capable of afflicting each other.
Related to its constant hunger, Entity 142 prefers to search for food in dark areas, as hunting in dark areas is thought to reduce the chance of prey escaping, with its success further complemented by its remarkable night-vision.
The hyphen between "night" and "vision" isn't needed.
After getting the kill, it will patrol a large perimeter around the carcass, displaying increased aggression, possibly in order to prevent its kill from being stolen, and following this behavior, it consumes the carcass.
The word "the" should be replaced with the word "a" since you aren't referring to a specific kill, but just one in general.
If it learns to associate humans with threats, it could turn from an entity killing machine into an everything killing machine, or worse, a human killing machine.
You overuse the term "killig machine". I also think that phrase is too informal. It would best to reword it into something along the lines of "it could stop killing just entities and start killing humans as well."
Into the Log!
Radio turns off, and Team Karl begins to walk towards the area where the sighting was reported.
The comma after "off" is not needed.
Kairo and Karl throw glass jars filled with firesalt at Entity 142, creating explosions that launch glass shards into it causing it to yell in pain.
Guess what! You actually are missing a comma here. You need it after "it" and before "to".
We need to tourniquet her arms, she's bleeding uncontrollably and won't last long if we don't stop the blood flow.
Define tourniquet in a footnote for readers. Completely unrelated to SPaG, I find it funny that he just suddenly turns into an emergency room doctor.
Karl uses gauze to cover up the stump of Nova's right arm, and applies pressure to the wounds on her left arm, while Kairo creates an improvised tourniquet using a pipe that detached from a machine and an emergency roll of gauze.
You don't need the comma after "arm".
The team arrived at Base Gamma-B at 07:46, and Nova's right arm was amputated and replaced with a robotic arm taken from Level 3.1 after two and a half hour, and her spine was repaired after six and a half hours.
I just don't like how long this sentence is. I would get rid of the comma and the word "and" after "hour" and replace it with a period. Then you need to get rid of the comma after "07:46".
Alright. SPaG critique-wise, that's it. I do want to point a few more conceptional problems I noticed while I was breaking your article down line by line.
It is generally apathetic towards humanoid entities, such as Blanche or Facelings, and will usually ignore them unless provoked or desperately hungry.
I imagine this entity would never be able to enter Level 906 since it wouldn't be allowed by Blanche. Therefore, I don't think you should use Blanche as a valid example.
Additionally, after Encounter Report 142-1, there is thought to be a layer of chitin1 underneath skin that protects it from projectiles and explosives.
I think you should add a detail using a comma to the end of the sentence clarifying what makes people/researchers think that it may have a layer of chitin underneath its skin, such as ", due to explosives not affecting it".
Alright then, you've included your license box. You've got it well organized. Tell me once you're done going through and correcting these SPaG errors and I'll see about a greenlight. I'll pm you the password to post your article then, as well.