This is the final time the library appears in a season premiere before getting destroyed by Tirek in the finale.
To activate Zecora's potion, Twilight uses the same dark magic from "The Crystal Empire - Part 2".
Discord is summoned almost similar to how the Mane Six released him in "Keep Calm and Flutter On", having almost the same exact poses as that moment as well. Twilight's pose in particular is edited to have her wings.
This two-part season opener revolves around the Summer Sun Celebration, just like the series premiere.
Just like "Magical Mystery Cure", the Elements of Harmony are kept on a display in the library.