Pinkie Pie. A pony who is random beyond belief and even rips apart reality itself. She is truly a master of her fate and lets no pony or anything tell her otherwise. She has all sorts of neat abilities and doesn't flaunt them on purpose.
Yet, one of her abilities she keeps a mystery from every pony else. A ability that would shake the very foundation of the pony world. Of any world for that matter. It's the secret to why all of her concoctions, hers and the cakes, are so good. The mystery behind it is a lot more... disturbing than you would have guessed.
She even gave everypony a hint at the last Halloween event.