Enigma is a new arrival to Ponyville, but after she goes to sleep each day, she's forced to re-live that day all over again, and nopony can see her or interact with her in any way. After the day is re-lived, she wakes up where she'd been before she had to re-live her day, but as if she'd never been there.
Special thanks to Ink for her cover art and for making ThatScootaloo, my favorite Tumblr ever! It doesn't matter if she doesn't update it anymore, I still love it to death.