I've been thinking a lot about how Mary Sues and how they relate to my fandom, and I realized that the bar is in a very funny place. I'd love to hear some thoughts about this. There is a lot of "normal person gets sucked in" and "the characters end up in our world." Possibly because the video game world ranges through "swords and sorcery" to various flavors of schizo tech. These are still fun stories. The main characters are insanely powerful vampires, and the human supporting cast are the most powerful sorcerers alive. The required powers of any normal person include a reason not to be eaten and a reason why anyone would notice them. It's like trying to convince a fisherman that you're a magic fish when everything that is edible can talk. Anyone from our world is automatically in Sue territory, but a lot of them are interesting and well-balanced otherwise. Likewise the stories still tend to carry tension and conflict. They are similar to Gravity-Sues but different enough that I'd like to call them Load-Sues. These are some of the standard setups I've seen. The characters are either slightly OOC or under subtle mind-control that can allow them to act almost completely normal, except with why they don't just eat or ignore the Sue. The decent ones as a whole are very romance-light, while the bad ones have a higher romance concentration. (I have seen one fic that predated Twilight, but is about the same setup.) Other times, the Sue is part of the plebtonium that brought them there, they are immediately aware of it, and put the Sue through a very scary journey so that they can go home. (The only fic I've found where the Sue goes into the world and is important plebtonium... is the one I'm trying to make into a decent Discontinuity Fic, and she goes completely background after the first part.) The only readable fic I've seen where the modern person survives by sheer badassery was when that person was Lara Croft. _____________________________________________ As far as OC's that are supposed to be from that world, the only way to tell is by seeing how well they match up with the cliche Mary Sue template. Overly long descriptions, rules of reality bend for them, their screen time overstepping how interesting they are...
You say fandom, so I assume fanfiction, yes? Just skip OCs. Nothing wrong with them in a strictly literary sense, but they are culturally incorrect. Folks read fanfiction to see the action and chemistry between canon characters. OCs are not really something worth putting a lot of trouble or thought into. OCs tend to be in badly written fanfiction, but that's a corollary of the writers being young and not realizing what it is readers are interested in. Gotta write fanfiction for the readers, not the writers. Just how fanfiction works...
I quit writing females in fanfiction period. In the fanfiction universe, no matter how we written they are, even canon female characters seem to always get damned with the title of Mary Sue.
I have a fundamental disagreement about OC's in my fandom. All of the canon characters except one are dead, (most died on-screen twice) and it would be limiting to write anything completely in-universe without introducing new characters or at least naming someone who only existed in a vague sense. Continuation fics need new allies and enemies, lower-deck and prequel stories need characters who would be dead by the time the official story starts. And when I call a character a Sue in my fandom, I find that maybe I need a different word to differentiate between annoying types and the good types. One of my favorite stories is about a battered wife who uses the games as escapism until one night the game characters come into the real world and add to her hell. She has Sue-powers, but it's still well-written. Other than that one with the cats, I admit that there aren't as many decent serious real-world crossovers as I remember. (Can't find the one with the minivan.) There are lots of funny insert fics and non-sues that get slaughtered. I once wrote in an illegitimate son for a canon character. People didn't seem to mind. There is also an amazing story that happens to contain a female clone of the main character but I wouldn't call her a Sue.
Most readers would prefer to read prequel or interquel fics about the canon characters than a continuation fic with OCs. Not disparaging your work, which I haven't read. It may be better than show. Just pointing out what fanfic readers are primarily interested in: the characters from the source material.
I've read through this a couple of times, and yeah, I think you need a different term for whatever character(s) you're talking about. There aren't "good" Mary Sue's - they're bad by definition. Female OCs are something else entirely, so maybe that's what you mean (never heard of the fandom - or many of the fandom-specific terms - so can't help on specifics there).