The one-shot story is based off the early spoilers for Episode 25 of Season 5, the Cutie Remark, as well as my own little headcanon as to what I think the show will go for. Also Days of Futures Past might have possibly helped inspire it too.

After a devastating battle with Starlight Glimmer ends in the Mane Six's defeat, Twilight gets hurdled back in time by Starlight in an attempt to erase her from history. What happens in the moment that Twilight was sent back to could change the course of Equestria forever.