WRITTEN BEFORE SEASON 5!!!
Without altering anything canon up to season 4 (though the movies are kind of skipped over, sorry), I manage to completely rewrite everything that happened. No, seriously. And it all started based off of Discord's photo-bomb in Fluttershy's window during the season 4 theme.

What if, rather than leaving with Celestia after he was reformed, Discord ended up staying at Fluttershy's house, unknown to any of the other ponies? Chaos ensues. (Pun intended. )

Definitely a Fluttercord.

After being away from her friends for awhile, Rainbow is faced with the challenge of earning back the strong friendships she once had. Will she be able to get things back to the way they used to be, or will her pride get the best of her?

Dear Discord,

I'm sure you have found yourself rather bored as of late, seeing as you have given up your true nature to stay reformed. So I have a project for you.

I'm awful curious to know what you do in your spare time, so I'd like you to keep a journal from now on and update me weekly. It will be a good way to kill some time, and it will help me keep tabs on you as you adapt to your new lifestyle. Think of it like a sort of Reformative Exercise.

You can send me your letters via dragonfire, which I do believe you are more than capable of doing so with your own magic. (If not, I'm sure Twilight will always let you borrow Spike,)

I'll be expecting your first letter soon!

- Celestia