A lot happened to Twilight Sparkle the year before she made the transition to Ponyville, before she realized the value of a friend, and before she saved all of Equestria...

After a chance encounter with "Rainbow:" an enigmatic, amnesiac pegasus mare with a rainbow-striped mane and a knack for mischief, Twilight begrudgingly finds herself overseeing her recovery, all while questions keep surfacing. Like who is she? Where did she come from? And more importantly... why can't she get her off of her mind?

As days turn to weeks, and weeks turn to months, destinies are revealed and the past is dug up as Rainbow's memories begin to resurface; and as sinister forces set their sights on Equestria, Twilight and Rainbow find they must overcome themselves in order to become the heroes they are meant to be.

Edits for the story provided by xgfhj.

Sequel officially now in progress exclusively (for the time being anyway) over on my patreon.
Check out the sneak preview here.

Princess Twilight Sparkle has a problem: she's possessed by a question. It came from a silly little book. Now, after a week of poor sleep, Twilight relents. She has to answer this question, even if it kills her.

Okay, so it won't kill her, but Twilight is going to have to violate one of the biggest pony taboos in existence to do so. That's okay. It's for science!

original author wille179

This is a fic based on the Time Loop Files, the format of which was first codified by Innortal on fanfiction.net.
Here's a brief guide.
The basic idea is, one character (the Anchor, usually the main character of a fictional setting) is looping back to the very first moments of their parent series every time either they die or some kind of time limit expires. They of course end up monumentally stir crazy given enough time.
Eventually others start to loop as well.
The reset is not always perfect. Sometimes a loop's history will be different to the "prime" loop, or canonical plot.
"Crossover" or "Fusion" loops also occur, randomly. These can involve the home loopers having a guest, or the anchor for one universe spending time in another, or replacements of one character by another.
Vacation Loops are where the Anchor (or others) decide/s "buck it" and lets off steam by doing whatever comes to mind. There's little or no attempt to maintain the original timeline.

In addition, and particularly more recently, it should be known that this story has a collaborative element to it - people may submit loop ideas or loops, ideally at the Spacebattles thread (a link to the current version of which is on the Trope page), and they may become included.

There's two page image options, thanks to Filraen - the current page image has been edited by the original creator from this work of theirs.. The other one is here:
http://hourglass-vectors.deviantart.com/art/MLP-Loops-466030169