This story is a sequel to MLP: FIM: The Vengeance of Kul'as
Kul'as has been defeated, for now at least, and the town of Ponyville is celebrating Nightmare Night as victory with him defeated. Everyone is all dressed up ready to have a good time along with a costume contest with eyes on the prize, but giving Fluttershy an enchanted costume maaay have been a bad idea, especially since it's of Saddle Rager.
This could've gone a whole lot better.