Gustav Le Grand is the second griffon to appear in this series. The first was Gilda, back in "Griffon The Brush Off."
Friendship Report: Pinkie learned that you shouldn't jump to conclusions without getting all the facts right.
Amy Keating Rogers, the writer for this episode, claimed on her Twitter account that she wrote a scene where Twilight compliments Applejack about her self-control only for Applejack to admit that she did take a bite out of the cake but didn't leave any clues, but this scene was cut for time.
Even though the title of the episode is "MMMystery on the Friendship Express", there should be four M's, as that is the shortened version Pinkie Pie gives for the cake, the Marzipan Mascarpone Meringue Madness, or, as she calls it, the "MMMM".
When Pinkie sees the Marzipan Mascarpone Merengue Madness has been eaten, she emits her prologue gasp from "Friendship is Magic, part 1".