This is a Fallout: Equestria and Harry Potter Crossover, inspired by Harry Potter and the Crystal Empire for those curious.

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What if, in the battle against Quirrel, Harry accidentally smashed the Philosopher's Stone on the man's head? What if this transported the entire school, along with all of the lands belonging to it, into the Post-Apocalyptic Wasteland of Equestria?
And what if all of the students, teachers and Ghosts got ponified in the process? Well, Harry has some other problems to boot, like figuring out what to do in this new world, and managing as both a Alicorn, a female at that, and one of six no less, as well as trying to keep the school and his friends safe.

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So, we're above 100k in length, I'm pretty proud now :D
Average chapter length so far is 4934.9545454545 as of chapter 22