Takes place during the Season 5 Finale. (And hints of EqG: Friendship Games)
Sunset Shimmer is out of space in her journal for communicating with Princess Twilight. On a whim, she decides to return to her homeland for a replacement. Unfortunately for Sunset, a pony named Starlight Glimmer was busy enacting revenge, catching Sunset in the crossfire and placing her in a different timeline than she expected. With no Elements of Harmony, no Princess Twilight, and no clue, Sunset must reunite the main six, save the timeline, and find a way home... eventually.