Epilogues · 9:02pm Jul 31st, 2016
As you can probably guess, I've had epilogues on my mind for the past week or so, largely because so many readers think that Transdementia needs one. As it happens, I did have an idea for an epilogue... but when it came time to write the last chapter, it seemed to work better to have Surprise make her introduction before Pinkie Pie left. I also toyed with the idea of having the scene with the return to Equestria serve as an epilogue, but let's face it, if you didn't think it worked as the final scene of the final chapter, you won't think it works as a stand-alone epilogue.
The whole point of epilogues is to clean up loose ends, and to be honest, I can't really think of any potential loose ends that actually need to be cleaned up. Several comments suggest that Discord's reveal to the rest of the Mane 6 would work, but I doubt anyone would have trouble guessing what their reaction would be (and besides, it has little to do with the plot of the rest of the story). I could, perhaps show Sunset being taken to prison and dwelling on her ruminations, but that would only work if I was using it to set up a later story, and as of this writing, I don't really have any ideas for the next story--at least, none that could be teased without feeling awkward and forced.
I get that you think the ending's abrupt. To be honest, I don't think it's perfect, either. However, at this time I can't think of anything that wouldn't just replace one set of imperfections with another. If I do manage to come up with an idea that I like, you can be sure I'll implement it.
EDIT: Sigh... I don't know why, but for whatever reason, writing down all the reasons I'm sure a problem is unsolvable always seems to convince my recalcitrant brain to come up with a solution. I've changed the status of Transdementia back to "Incomplete." (Sorry to inconvenience those who already sorted it into "Completed Stories" bookshelves.) I hope this idea works as well as I think it will.
Why not a story where Penny and Pinkie are babysitting Flurry Heart?
Makes sense.
Nothing quite like talking a problem out to perspective on it.
I personally found the ending to be nice and tidy as it was.
I'm a bit late to this party, but in my opinion, there was nothing wrong with what you actually wrote. It was good, as far as it goes. With that said, I can't help but think of how much fallout there is going to be on the human side of the mirror, at Canterlot High in particular, but also around town when word of what happened spreads. Between the pitched battle, the overt use of magic, the presence of aliens, and Surprise's sudden appearance, there will be a lot for the media and rumor mill to chew on. Things on the pony side won't be quite so dramatic, but Sunset's return and trial would probably at least make some major headlines.