Well, that certainly was different. I can't believe they went there with turning Flutterssy into a batpony, but it was a lot of fun.
Not much to say about it otherwise, except that it had a ton of season 1 callbacks (yay) and though the plot was really slight, it was well-handled. And once again it was conflicts between members of the mane 6 (and a failing by Twilight in particular) that drove the action; they'd largely abandoned that storytelling approach for seasons 2 and 3, so it's nice to see it making a comeback.
One odd thing: the per-release info on this episode indicated it was written by Meriwether Williams, and she's credited with the song lyrics during the closing credits, but the "written by" at the opening says Meghan McCarthy. I wonder what happened there?