RPC Authority

I don't want to dissuade you since you're clearly very passionate about this, but I'm not exactly sure what you're trying to do here. We're left with too little details for a compelling mystery: How does the note connect to the monster? There's clearly a story waiting to be told, but the article has yet to deliver. Also, everything in the addendum sounds like it should be in the containment protocols.

Don't give up, we all struggle with our first article.

It is effectively impossible to completely contain RPC-XXX on a global scale. Authority personnel who report symptoms consistent with RPC-XXX sufferers are to be informed of RPC-XXX’s hunting methods to inhibit unnecessary casualties. (See Addenda.)

Consider:

RPC-XXX cannot be effectively contained at the present time. Authority personnel who report symptoms consistent with RPC-XXX-A instances are to be briefed on the nature of RPC-XXX. For a more detailed report on RPC-XXX's behaviors, please refer to the addenda attached to this article.

Civilians who report symptoms consistent with RPC-XXX sufferers are to be placed under observation in Authority hospitals, under the guise of sleep therapy.

Civilian deaths believed to be caused by RPC-XXX-B are to be given non-anomalous causes of death by implanted Authority morticians.

Firstly, I would merge these two sentences together. Then I would rephrase them like so:

Civilians identified as instances of RPC-XXX-A must be relocated to the nearest on-site medical facilities. RPC-XXX-A instances are to be falsely informed that they will undergo non-anomalous treatment and will be amnesticized upon release. Fatal incidents caused by RPC-XXX are to be issued appropriate cover stories to mislead the public.

Secondly, the Authority usually amnesticizes civilians, which is why I included it in my hypothetical revision of the text.

RPC-XXX is a predatory dimension that manifests in human dreams. RPC-XXX’s first manifestation in a victim (hereby referred to as RPC-XXX-A) is the only manifestation that has been properly documented.

Consider:

RPC-XXX is an alternate spacetime which enters and abducts human subjects (hereafter referred to as RPC-XXX-A) undergoing the REM phase of sleep. Currently, all documentation of RPC-XXX comes from RPC-XXX instances undergoing an abduction event.

I have to ask: What's going on here? Are the subjects experiencing this alternate dimension in their dreams, or are they abducted and brought there? I went with the latter interpretation, so feel free to correct me.

RPC-XXX can only first manifest when all of the following are true:

Consider:

RPC-XXX can manifest under the following conditions:

RPC-XXX-A is not being observed,

Consider:

RPC-XXX-A is not under direct observation (by a sapient? sentient? lifeform),

RPC-XXX is not currently manifesting within an individual 500 or fewer meters from RPC-XXX-A’s location,

Consider:

RPC-XXX is not already manifesting within an individual within 500 meters from RPC-XXX-A's current location,

RPC-XXX-A is not currently under the influence of mind-altering drugs,

Question: Since the subject's mind would be more open to suggestion because of the drugs, wouldn't it make more sense for it to prey upon them while they were high?

RPC-XXX is married, was formerly married, is pregnant, or has at least one child.

Consider:

RPC-XXX-A is or was married or parent to at least one (biological?) child

Following RPC-XXX’s first manifestation in RPC-XXX-A, no other dreams will ever be experienced by RPC-XXX-A.

Consider:

RPC-XXX-A will experience no other dream following the first manifestation of RPC-XXX.

Also, I would merge this sentence with the following two sentences so you have a proper paragraph. Alternatively, I would merge this paragraph with the first paragraph in the description section since they both discuss similar topics.

RPC-XXX physically resembles a long hallway that is constantly immersed in fog. The specific appearance of the hallway appears to vary between manifestations, but will never have any windows or timekeeping devices.

Consider:

RPC-XXX's physical qualities vary from encounter, however, the area always resembles a windowless long hallway constantly immersed in fog.

RPC-XXX is of infinite physical and temporal length; the end of the hallway can not be reached and RPC-XXX will not terminate until RPC-XXX-A wakes.

Consider:

RPC-XXX has no known endpoint and is hypothesized to be infinite in length. RPC-XXX will not terminate until the subject awakens.

RPC-XXX-A will appear at the beginning of the hallway in formal attire, and will be holding a briefcase in their nondominant hand. RPC-XXX-A will then open the briefcase and read the contents of an envelope contained inside:

Consider:

RPC-XXX-A manifests at the start of a hallway in formal attire and a briefcase in their nondominant hand. Opening the briefcase reveals a letter inscribed with the following text:

RPC-XXX will contain several rooms to either side of the hallway. Each of these rooms contains a repeating showcase of one subjectively important event in RPC-XXX-A’s life. These displays are more accurate than RPC-XXX-A’s own recollection of these events, and can be freely paused, rewound, or slowed down by RPC-XXX-A.

Consider:

RPC-XXX contains several rooms adjacent to each other throughout the hallway. The rooms contain iconography and items relevant to the life of RPC-XXX-A. The displays are often more accurate to real events than RPC-XXX-A's own recollection. These events may be paused, rewound or slowed down by RPC-XXX-A.

The rooms of RPC-XXX constantly exude a rich and pleasurable scent of lavender, commonly accompanied by a deep feeling of guilt, regret, or other emotions that may drive RPC-XXX-A to remain in these rooms. It is extremely difficult for RPC-XXX-A to willingly exit these rooms.

Consider:

The rooms of RPC-XXX exude scents often compared to lavender and often accompanied by deep feelings of guilt, regret or other negative emotions which may prevent the subject from leaving. Leaving a room has proven extremely difficult for RPC-XXX-A instances.

The light fixtures illuminating the internals of RPC-XXX will intermittently cease functioning. The rooms within RPC-XXX will remain freely accessible and lit during this time, and RPC-XXX-A will be driven to take shelter in these rooms until proper lighting is restored. While RPC-XXX is unlit, several extremely loud footsteps and pained vocalizations will be perceived just beyond the walls of RPC-XXX. RPC-XXX-A will most commonly wake up during this time.

Consider:

Light sources illuminating RPC-XXX's interior may temporarily cease functioning, but RPC-XXX rooms will remain accessible despite the changes in lighting. While unlit, footsteps and pained vocalizations with no identifiable source will become audible to RPC-XXX-A instances. Most subjects awake during this period.

If RPC-XXX-A wakes up while within a room in RPC-XXX, RPC-XXX-B will manifest.

Consider:

If RPC-XXX-A was situated in one of RPC-XXX's rooms prior to awakening, RPC-XXX-B will manifest.

RPC-XXX-B is a selectively intangible, invisible, and unstoppable humanoid. Upon manifestation, RPC-XXX-B will become aggressive and ████ ███████ ██, ████████████, typically until death, █████ ███████ █ prior to violently ██████ ███████. Neither observers nor RPC-XXX-A will survive this encounter.

The biggest problem here is the unnecessary censorship. Either describe the things this creature does, or don't keep the audience guessing. Also, is it just a matter of fact, an unspoken law of physics, that it's impossible for the subjects to survive, or have we just not discovered any survivors yet?

RPC-XXX cannot be effectively contained at present.

Try:

RPC-XXX is currently uncontained. Containment methods are under review.

RPC-XXX-A instances are to be falsely informed

You mean to say civilian instances or in general? Cause the way it's worded here would contradict the paragraph before.

falsely informed that they will undergo non-anomalous treatment and will be amnesticized upon release

So are common folk just told they'll be amnesticized? If that's not what you meant, keeping these two statements in the same sentence suggests that, and I advise you separate them in two. If you did, this info is typically told on a need to know basis, so would civilians need to know this?

RPC-XXX’s skin is coated in or composed of a substance

Indecisiveness in a technical report has it lose that technical clarity. In which case try:

RPC-XXX's husk absorbs all light when outside of RPC-XXX-B

RPC-XXX is capable of stalking and abducting human prey (hereafter referred to as RPC-XXX-A) undergoing the REM phase of sleep.
RPC-XXX-A instances currently being stalked by RPC-XXX commonly report constant feelings of dread or unease, along with an overpowering feeling of fatigue, and will be unable to find the source of these feelings. RPC-XXX-A instances are unable to perceive RPC-XXX prior to being abducted.

Try:

RPC-XXX predates on human subjects (hereafter referred to as RPC-XXX-A) by stalking them and abducting them in their REM phase of sleep. When stalked, RPC-XXX-A instances report feeling constant dread or unease, along with a debilitating sense of fatigue. Notably, no victims report record sign of RPC-XXX prior to abduction.

RPC-XXX can only abduct an individual when all of the following are true:

- RPC-XXX-A is not being observed,
- RPC-XXX-A is unarmed,
- RPC-XXX-A is married, was formerly married, is pregnant, or has at least one child.
When attacking, RPC-XXX will latch onto RPC-XXX-A, and both will vanish. RPC-XXX-A will then reappear within RPC-XXX-B.

Try:

RPC-XXX has shown pursuit only when the following RPC-XXX-A conditions apply:

- Subject is not under supervision
- Subject is unarmed
- Subject was married, pregnant or has at least one child
RPC-XXX will latch onto RPC-XXX-A and vanish after a successful pursuit, teleporting them to RPC-XXX-B.

The light fixtures illuminating the internals of RPC-XXX-B will intermittently cease functioning. The rooms within RPC-XXX-B will remain freely accessible and lit during this time, and RPC-XXX-A will be driven to take shelter in these rooms until proper lighting is restored.

I assume this intermittency only occurs within the hallway? It should say so if that is what it has in relation to the statement before it. As it stands though it comes off as confusing.

RPC-XXX-A will reappear in reality at this time.

Try:

RPC-XXX-A will remanifest to where they were originally abducted.

I opted not to cover the rest as they just repeat same issues I've addressed above. Follow that pattern with the rest of the article and it should be good.