King Sombra, the tyrant of Crystal Empire is back, only to be imprisoned by princesses and put through reformation with Twilight Sparkle as his teacher. Can somepony with heart as black as night be reformed? Twilight believes so.
"Anon, you must distract Chrysalis for us so that we could grab that bell! You need to get her attention somehow- wait! What are you doing? That's not what we meant at all!"
Spike is the guest of honour at a high society party important to the Council of Friendship. It'll end in political disaster if he doesn't find a date for the dance. Luna magically disguises herself as his date but ends up stuck in her new form.
This Hearts and Hooves Day, Twilight is alone. Not a big shocker, but it helps her realize something. That without her friends- she really hasn't grown anymore as a mare than that of a filly... That's where (or 'when') the Doctor comes in to help.
The fall of the unified Equestrian republics results in a vicious civil war. A dark take on the world of Equestria, inspired by the vicious brother war of the former Yugoslavia - as written by an Eastern European who grew up in such an era.
The Crystal Empire finds itself in the middle of property dispute when a representative from the north comes in, claiming that Equestria doesn't own the land. Who does? Canada, apparently.