Picture this: What would have happened if Twilight's Kingdom had gone just a little differently? Well, for one thing, there would be no reason for this book, but also, there would be chaos in Equestria. What kind of chaos?
Demonic Princess Celestia kind, of course.
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I recently realized that I haven't provided a link to the sequel, A Good Mare Goes To War. Silly me!
The thing I just mentioned