I actually thought they did a good job with Dash today. She's always had a powerful winning streak in her, one that can be inherently at odds with her loyalty (because one does not always allow for the other, as today showed). She also seems to be aware that she's pretty consistently always right on the verge of really breaking out and making it to the big leagues, but she always ends up staying small-time in Ponyville (so to speak, of course; she's also a world-famous hero several times over, but the show seems to play fast and loose with how the Mane 6 are treated by other ponies about this sort of thing). I like that they put all that to the test, especially to present her with a clear case of testing her Element (which seems to be the trigger for each key to the Mystery Box. I expect Pinkie's key to pop up at the end of the Weird Al episode).
Fluttershy, meanwhile, was probably just talked into the whole thing. She's not exactly difficult to convince. Why they didn't choose Twilight over Bulk Biceps, though, I have no idea. She's got wings now. Take advantage of that.
Quite liked the background shots of the Griffons. It's about time they made a comeback.