This story is a sequel to Ordinary Nightmares

Derpy has had a lot of misadventures. Amid them all have been moments of happiness, sadness, hope, and despair. She has come face-to-face with mad scientist wizards, tea-loving pirates, changelings, ancient dragons, and even the breaking of reality itself. All along, there has been a pervasive sense in her mind that it was all beyond her; that simple little Derpy Hooves from Ponyville wasn't meant for moments like these. Somehow though, against all odds, she has succeeded time and again.
Now, that peculiar tendency brings Discord to ask her assistance in a unique crisis of his own making. Aeons ago, he made a machine with a unique ability: the power to invert the probability of the entire universe. It is a machine that makes the most unlikely the most likely, and the most probable all but impossible. If it becomes active, the consequences will be catastrophic in ways that defy imagination.
Only a pony with almost no chance of stopping such a contraption has any chance of stopping it at all. The best-laid plan will go awry, and the greatest hero will doubtlessly fail. Fortunately, there is one pony in Equestria who was never meant to be a hero.

Cover art by tarantad0 of Deviantart