I didn't observe any changes in Pinkie Pie or Fluttershy from what we've witnessed in previous episodes. I mean, at least Fluttershy's just trying and failing to be assertive like usual instead of going over-the-top like in "Putting Your Hoof Down".

I agree though that King Sombra wasn't all that impressive. I mean, as an embodiment-of-evil he fit the bill pretty well, but I feel like we didn't see enough of him to really view him as a character rather than just a mysterious threat.

I don't really see how Fluttershy changed, other than that her character development tends to regress back to complete timidness. That's not atypical for cartoon characters though. Pinkie definitely seems more goofy than quirky, but I don't find that jarring just yet.