Just kidding, it's Spike and Rarity co-starring in an episode in which basically no one else appears (each of the other ponies gets one brief scene, except for Twilight who gets two).
Just kidding about being kidding, this is *totally* the spell Sombra used to create the Crystal Empire. Rarity was about ten minutes away from going full 'cryysssstaaals' by the end there.
I liked how we're basically following the villain around while the hero (Twilight) runs around like a chicken with her head cut off trying to figure out what's going on.
The puppet guy was also pretty cool, although at the same time he was ridiculously uncool and creepy.
The birdhouse was my favorite bit of wandering mayhem. Well, that or the roads, especially in the long shot.
The weirdest part was that Rarity started changing ponies into other ponies and what the fuck? Maybe she was just transposing them, and somewhere else in Equestria the classical orchestra was suddenly +1 Mariachi band? Oh, who am I kidding. They were probably transformed by Rarity, and then sent back to the mirror pond by Twilight who assumed they were dark magic constructs.
Overall... it was probably as good as a Spike + Rarity episode can be. If you actually like Spike and/or Rarity... you'll probably hate it. n.n
I'll give it a 2/3 and then remind myself that I've been giving *everything* 2/3 and that I should probably go and watch everything back to back to do an actual comparison.