Here comes new extra bosses, Starlight Glimmer and Daybreaker!
Both pretty fun and really hard in different way.

Starlight Glimmer is kinda RNG battle. Her attack itself are not so hard to dodge, but she makes 1 or 2 illusions that attacks you at the same time!
Every time you must recognize all Starlights' attacks, and decide how to dodge. I gotta say that 3rd phase is just crazy :O
And she has a cool counter-attack. That's sooo cool but that's why you shouldn't use any familiars or continuous skills against her.

Daybreaker doesn't have so various attacks like Nightmare Moon, but each attacks are really speedy, aggressive, and hard to dodge. 
Also like NM, Sometimes a random bullet spawns (not totally random and it often spawns at offensive spot) but this sun-shaped bullet chases you! That's really a problem and why this dark-Celestia is sooo strong.