(Notice: MLP S9E1 and S9E2 are called "The Beginning OF the End." This is "The Beginning AND the End.")
Twilight Sparkle time travels. She was TRYING to send a letter to Princess Celestia about to incoming return of Nightmare Moon. She DID travel about twenty-eight years into the future.
(Crossover between MLP S1E1 "Friendship is Magic, Part 1" and MLP S9E26 "The Last Problem")
EDIT 3/4/20: WHAAAT?! 56 bookshelves and 28 tracking as of now?! This has got to be easily my most popular story. Many, many Pinkie-sized hugs to you all!