Basically it's a what if scenario in which the mirror portal opens up in Bullworth Academy instead of Canterlot High. and i mean a version of Bullworth run and inhabited by the students and faculty of Both Canterlot High and Crystal Prep.

Dear god, Imagine what Twilight and Sunset's experiences during their time there would be like?

Sunset would definitely have a field day on Bullworth of all places and Sci-Twi will probably have PTSD from the constant harassment.
Honestly now that I think about it, Sunset would absolutely get along with Gary and I'm having a hard time deciding if that's neat or worrisome...

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Probably worrisome considering that this is pre-RR Sunset Shimmer we're talking about.

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i wonder how the rest of the mane 6 native to the human world would be like in this setting. Their personalities and positions in the academy and all.

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Ok it's been a LONG time since I last played Bully so bare with me here...

Rarity would be with the high-class students (obviously) but they are normally associated with botanic classes so maybe Applejack wouldn't be too far off, although she's more likely to be helping in the families own garden than torturing herself with those snobs.
I think there IS a candy shop somewhere in the city although I could be wrong, in which case she's more likely to be there or in the lunch hall... Or with the others I donno
Rainbow Dash would be with the sports club and knowing her it's more likely because of boxing rather than American football although she could be doing both just to say she can.
As for Flutters... The only places I can think of is either the park or close to the coastline maybe giving seeds to the pigeons and seagulls.
Sci-Twi would be with the nerds (again obviously) which funnily enough would explain her antisocial behavior because good god these poor bastards just can't catch a fucking break.
Sunset Shimmer would be with the bullies, probably working along with Gary for the sake of amusement only to be both disappointed AND pissed because spoiler alert: Gary is in fact... Schizophrenic!!!