So, it looks like a couple of our more popular background ponies and a couple of lesser-knowns have now played a significant role in an episode where its main character is still one of the Mane 6!

(And I spotted my favorite background pony -- still being a background pony -- in the exterior shot where MD enters the library as Spike, Twilight, and Menu-ette watch.)

Still waiting for Sea Swirl, Lightning Bolt, Medley, Raindrops, and Cloud Kicker to have their day in the spotlight.