The music that Rarity chooses for her performance was "The Waltz" by Tchaikovsky, which is mostly heard in the famous play, Swan Lake.
Fluttershy's inhaling when she is about to cheer for the last time is actually Pinkie's huge gasp from "Friendship is Magic, part 1" played backwards.
Derpy Hooves, the fan-favorite pegasus with crazy eyes, can be seen at 06:28 and 13:14. The episode is otherwise filled with 'normal' Derpy clones visible in the audience in its second half.
Friendship Report: Rarity learned to be there for her friends, while keeping her hooves on the ground (literally and figuratively).
When Rainbow fails at her sonic rainboom in the beginning, she has one front leg outstretched; when she completes it successfully to save Rarity, she has both front legs outstretched.