Feel free to use any of these.

#1: Celestia farts during day court... a lot.
#2: Twilight goes back in time to date herself.
#3: Ponies are cursed so that they poop themselves whenever they lie.
#4: Celestia admits to being the true father of the Cake Twins.
#5: Gummy dies (sad fic?).
#6: Twilight imposes a "friendship tax" that requires ponies to hug a stranger at least once a day.
#7: Luna is secretly the cause of all the wet dreams of the stallions she thinks are cute. (It's how she gets her "relief")
#8: Big Mac is genetically a unicorn, but his visible horn gene was repressed. One day he discovers he can perform magic.
#9: As fluttershy learns the joys of being sassy, she decides to change her name to Fluttersass. Ponies read it wrong.
#10: Thorax lets Shining Armor know that he's his is son (one of many).
#11: Twilight gets demoted from princessship. Celestia removes her horn.
#12: "Cutie Mark Crusaders, Paid Assassins! Yay!"
#13: Twilight discovers that no one in Ponyville can be killed (or even seriously injured). Risky experiments ensue. The CMC volunteer a lot.

More to come.