Twilight Sparkle never meant to do anything wrong. But then again, all magical mistakes are caused by ponies who have no idea what happened. That's why they're called mistakes. The only difference with Twilight's mistake is that it accidentally sort of turned her into Princess Celestia. And now she doesn't know how to change back.

Twilight wakes up and finds out that she's changed back into a filly! What kind of trouble will she get into? How will her friends react?

My name is Rainbow Dash and today I learned something new. I learned I'm actually a changeling. You'd think that would be something you would already know. I just learned it now when I saw my true self for the first time. How did I come to replace the real Rainbow Dash, and when? And why can't I remember it?