I might have missed a few things, especially since I don't know much in the way of the context, but since this was the Board's first introduction to the Sue Slayers as such, I'll just look at it as it stands.

The narration seems to be, to use a term, all over the place. Especially during the first part, in which it seems as though the narrator is just constantly getting distracted, which really isn't helping set the tone. The exposition is often spat out in short bursts that seem unfinished, since they usually just generate a confused question or two before the story switches back to something else, save that section right before the team enters Indeterminate High School Fandom when the exposition begins describing the team as though it doesn't want to do so and would rather be somewhere else. That's really the only reaction I get from that scene. When character introductions are that brief, that cut off from the actual flow of the story, and ended using phrases such as "so, yeah" and "It's weird.", it looks as though the narrator realized there was more to exposit, didn't want to insert anything into the later or earlier action, groaned theatrically, and just dumped all of the character establishment between two sections of the plot so that it could get on with its day. That was the first time most of those people had been mentioned. It should not feel like that, especially if these are central protagonists as the story seemed to indicate.

Oh, and related to the character establishment: when delivering traits such as "[] enjoys guns", "[] can be annoyingly sarcastic", etcetera, it's usually best to show an instance of the character behaving in that way and then reinforce it through dialogue and narration rather than having the narrator's telling us about the trait come first and the showing not ever going into play. It's better to let people form impressions on their own rather than telling the reader what they should be noticing.

The alternate universe Sue Slayers just seemed to come out of nowhere and vanish without affecting the story at all. They were around for, translated roughly into real time, about thirty seconds, and the only things they do are mention a "Canon Rebellion" and seem significantly less affected by meeting their alternate-dimensional selves than one would typically expect. Was this intended to foreshadow something? Are there meetings between multiple universes all the time in Sue Slayers? How is meeting an alternate self "cosmic irony"? What was the alternate-universe team even doing there?

This is going to sound a bit out of place, given the PPC context, but why did the team immediately go after and kill the Sue they found? She wasn't doing anything aggressive until they charged her with weapons drawn for no reason, there was no indication that she was breaking canon or that she would potentially cause of future problems for the team, and not even any confirmation that she was really a Sue and not just some sparkly but ultimately benign OC written into being by a naïve preteen. All we got was "Type 3 Mary Sue", which is apparently enough ground for sudden abandonment of the Squee-tracking mission until the offender was a hole in the dirt. What is Type 3? Is it a rank on a scale, or a recorded species, or a strata of Sue behavioral ranks? Are Type 3 Sues the "oh, sweet merciful heavens, they'll tear the world asunder unless we kill them right this instant" sub-type?

Actually, a lot of mentions were not explained or elaborated upon at all, which might make sense if we were expected to have read another story beforehand, but as an introduction, it just creates confusion. What's the distinction between the Squee colors? How exactly do the fangirls hop worlds in organized groups when they are "mindless, shrieking beasts"? How significant is promotion to X15a to X14b? What did that throwaway line about growing extra limbs by passing through a portal mean? Does the substance allowing the Sue Slayers to cross through space-time boundaries occasionally cause spontaneous mutation, or is it tied into that other throwaway line about people drowning when they walk through the portals? What exactly is the effect of the music? Does it disable the Sues, or give the assailants strength, or something of the sort? And if it does, why is the example given here a Katy Perry song? One would think that pop music would energize a Sue, not benefit her opponents. Can different genres of music produce different effects?

Basically, this was kind of a mess. Not an irredeemable mess, since many of its problems could be severely alleviated with a decent enough rewrite, but it leaves too many questions unanswered, has too-abrupt or unexplained introductions to almost everything that happens, tells rather than shows, and ends without the majority of its characters having done much of anything. I had honestly forgotten a few members of the team existed by the time they were brought up in the NAMES ARE CAPS-LOCKED paragraph, and they had only last been mentioned a page before. That might in part be due to my headache, but the storytelling doesn't help.