nearest MTF personnel shall be dispatched to intercept the SCP-XXXX-1 instances.

'the nearest MTF personnel shall be dispatched to intercept the SCP-XXXX-1 instances'.

You may also want to think about naming the MTF you're using - you can invent a new one, or you could see if one from this page will fit with your scip.

All recovered instances shall be photo copied to and cataloged.

'Photocopied' is one word.

Instances are to then be destroyed via complete incineration.

I'm not sure 'complete' is needed here. Just incineration is good enough.

any nearest Foundation agent

I would say 'any nearby Foundation Agent'

and tasked with collecting and documenting said instance.

'and be tasked with…'

Upon, transmutation of reward money, appropriate cover stories will be fabricated and disseminated and Class-A Amnestics deployed as necessary.

No need for a comma here - 'Upon transmutation of reward money, appropriate cover stories…'

when dialed by the intended target of the SCP-XXXX phenomena

'Dialled', and does this mean that only certain people are 'target' by this phenomena? If so, why? What makes these people different? Can a person ignore the poster? Can a person dial the number but not be undertaken by the phenomena?

All text is written in English with no consistency in content between events except for the promise of a cash reward, ranging in value from a few US dollars to [REDACTED].

I'm on the fence about this redaction - whilst it does add to the mystery, it feels a tad unnecessary. Just something to think about that I feel as a reader. This guide will help you figure out if it fits.

generate further from this epicenter at an indeterminate rate.

There must be some sort of idea of how far this distance is, in terms of radius, even if the rate can't be determined.

To date, the exact method of SCP-XXX-1 instances materializing has not been determined; they will not appear at a location directly observed by humans and any form of equipment monitoring the location visually will malfunction at the exact moment of occurrence.

Then how is it known that they appear at (roughly) 5am if they can't be viewed in some way? I understand they've used a method to measure the radiation, but I don't believe that means they could know they're placed there at 5am. If this is how it is determined, I think you should describe this with some more clarity.

An instance of SCP-XXXX-A is an animal currently under the care of an individual (henceforth refereed to as "the owner"). The first phase of an SCP-XXXX event's primary effect commences upon the owner's visual recognition and comprehension (if the owner cannot read English, they remain unaffected) of an SCP-XXXX-1 instance.

I read this a couple of times before I understood what you're saying, because the first line confused me. I think you need to separate the description of what SCP-XXXX-A is and the phases of SCP-XXXX. It gets a bit all over the place otherwise.

They will anomalously believe that SCP-XXXX-A rightfully belongs to SCP-XXXX-2.

You don't mention what SCP-XXXX-2 is at this point, so, again, you need to explain that at least a little before saying the owners contact -2.

So I would describe, even briefly, what -2 is, before you talk about contacting it. Hopefully it'll just mean rearranging some paragraphs and sentences, as I know you do go on to explain it.

in his early 40's dressed in fashion appropriate for the 1940's, with dark brown hair and blue eyes, and speaking politely in 40's era vernacular.

'1940s' and '40s' should be written without apostrophes. It's a common mistake, even taught in schools, but it should be without them.

in his early 40's dressed in fashion appropriate for the 1940's, with dark brown hair and blue eyes, and speaking politely in 40's era vernacular.

What if the owner is watching out for the car? Like when someone has something to be collected from Gumtree, I know a lot of people who peak out of curtains. Does it just appear a minute late or even a couple of seconds late when the person isn't looking? It doesn't mean you have to explain this, but you as the author should know the answer to this question.

the money will materialize inside the home of the owner.

Does the owner find this strange, or does the anomalous effect means they don't find it unusual?

If the transaction can't be completed 00:00 the next day, the event will spontaneously end.

What happens if this occurs? Again, you don't necessarily have to explain it (unless maybe it's an interview or test log) but you need to know what happens to the owner and SCP-XXXX-A.

The entirety of the rewarded currency will inexplicably be transmuted into [REDACTED] with a total mass equivalent to the that of the original currency.

Again, the use of this [REDACTED] could be misplaced. For example, it could be transmuted into toast, or SCP-447 or ten cats. It's not quite mysterious enough that someone could feel intrigued about what's hidden (this is just my opinion as a reader, not just a reviewer) nor is it vaguely clear enough that someone could guess what's hidden. I'm not saying you should get rid of it, but you should think about it, based on the earlier linked guide.

Owners under the effect of the second phase of SCP-XXXX will display signs of acute paranoia and will become extremely protective of their "reward" to the point of experiencing episodes of reclusion dedicated to watching over the biological material.

I'm not a huge fan of the driven crazy trope, but I think it works quite well here. People have misused it before, so it always makes me hesitate when I read it - but, again, I don't think you've done a bad job of it here.

Foundation agents were first alerted to abnormal events attributed to the SCP-XXXX phenomena by news reports originating from ████████ █████, Wisconsin during the summer of 199█ of possible cult activity after the sudden disappearance of feral cat colonies surrounding the area and the discovery of the remains of approximately ███ felines in the garage of a suburban family home.

This is a run-on sentence that should be split into at least two different sentences.

Foundation agents acquired all evidence from the crime scene and were able to obtain custody of the 2 suspects

Generally, with numbers, you should write out the numbers between one and nine, then use digits for 10 and up, unless using units where you should always use digits. So, in this case 'obtain custody of the two suspects…'

Interviews were conducted with both subjects, who were still partially affected by altered mental states associated with the second phase of SCP-XXXX events

Is it these mental health states, or physical issues from living in a house with x amount of feline remains in it that caused them to be hospitalised? This may be something you want to clarify if it occurs naturally, but, as with a few things I've pointed out, something you should personally know as the author even if you don't include it.

Through further testing of acquired evidence and the subsequent occurrence of further SCP-XXXX events, details provided by the subjects were corroborated.

I think the wip interview will help clarify this for me, but it sounds like a lot of this stuff was found out by The Foundation fairly randomly, by chance, whereas articles often work better if you can read between the lines to learn how The Foundation found out about this naturally. You hint at how it was discovered, but it's a fairly complicated line of events to clarify as anomalous.

Initially, MTF personnel tasked with SCP-XXXX containment were issued one (1) lab mouse with implanted tracking chips each for research purposes.

We generally don't do the numbers in brackets thing anymore - it's normally done for a specific or precise reason, like the amount of medication, not writing like this. So it would just be 'were issued one lab mouse…' However, I don't know if I would trust a mouse to induce such an event - there's not often 'lost animal' posters for mice. Maybe you should include earlier examples of supposedly missing animals, to show that it could be unusual animals too, rather than just cats or dogs. Honestly, it would see The Foundation using more common animals like cats/dogs to try and induce an event.

he was markedly more amicable while under these effects

This may be worth mentioning as an effect of SCP-XXXX, earlier on.

When reward money underwent transmutation, the entire population of lab mice at Site-██ was lost. Resulting biological material used to supplement D-Class food supply in an effort to cover the cost of training new lab mice for testing. Agent B████████ remarked that he felt like he "was having a little chit-chat with Mr. Rogers" before he was administered requisite amnestics.

I like this outcome. I like the whole audio part, actually. It felt very natural but at the same time, suitably unusual and anomalous. A seemingly normal conversation which we, as the reader, know is unusual, but it's easy to see how members of the public wouldn't find it all that unusual, until the point where the 'reward' transforms into something else.

Director firmly recommended that further testing involving SCP-XXXX and Foundation property should be prohibited. This recommendation was accepted.

Does that mean more experiments could be undertaken if personnel was willing to give up their own pet? That may be worthwhile exploring, even just as an addenda rather than a full audio or experiment log.

On June 21, 2014 at approximately 05:05 CST, an SCP-XXXX-1 instance in the form of a missing child poster was intercepted in ██████ County, Wisconsin. This represents the first iteration of a human SCP-XXXX-A instance.

Nice twist, I appreciate that a lot. Not starting with the most terrifying thing (which is an easy way out a lot of authors take) but subtly putting it in at the end, almost as a reward for reading that far.

All in all, I really enjoy this. I had to take a lot of breaks when reading it for various reasons, but it never lost my interest whilst I was reading it - despite its length, I didn't feel like I was slogging through or forcing myself to read it because I promised you a critique. It is an article I would willingly read on the site. You have a few things to fix in terms of missing words and the like, along with a few questions to think of the answers too, whether you include them in the article or not, but really, it's very close to being a final draft. I'll be willing to review any further drafts of this article you have, and/or when you include more addenda, interviews and the like.