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

What if Twilight was orphaned before her acceptance into Celestia's school for gifted unicorns?
what if she and the princess of the sun became inseparable? What if Twilight starts calling Celestia mommy after their lessons?
What if Celestia loves it?
Inspired by the cover photo

On their six month anniversary, Twilight and Celestia were enjoying themselves when a power surge drew their attention to the Tree of Harmony. To their shock and horror, the second they arrived the tree began to glow so brightly they were forced to turn away. When they were able to see once more, there were two fillies asleep under the tree; both had wings and a horn. Not sure what else to do, Celestia lifted the fillies onto her back. Once she climbed the stairs, followed by Twilight, she was very glad they were on her back and not within the grasp of her magic. The Palace of the Royal Pony Sisters was gone and the Everfree Forest was bright, filled with the sounds of birds' singing.

Twilight and Celestia stared at each other in shock. It was apparent that they weren't in Equestria anymore.

Cover Art drawn by my twin bruddah Otto

Lovingly edited Chap 3+ by Jumbled

Twilight and Luna become foals. Dark tag due to the actions of the characters of the story.
On hiatus because of life. Its been years still trying to find time. Sorry.
Editor/co-writer: StarFall13
Co-writer:Autum Breeze

Give a big thanks to them.

This story is a sequel to Celestia's Twilight

We all know the story. One thousand years ago Princess Celestia was forced to banish Nightmare Moon to the moon to save all of Equestria, but what if Luna had been hiding something from her sister, scared of how she would react? When Luna had no other choice, she cried out for Celestia and Celestia came. For one thousand years, Luna wondered what happened when Celestia left; now she's finding out...

But is it already too late, or will Luna be able to take the role she had so long dreamed of? The dream of being a mother?

editor Don't Look At My Name Bro! and RK I am lost without you!

Celestia had a niece once, not an adopted niece like Cadance, an actual biological niece, the daughter of Princess Luna. Sadly when Luna became Nightmare Moon her daughter took her mothers side and led the their forces against Celestia.

Princess Twilight was killed during that battle, or so history tells us...

Featured on the 11/10/2015! Thanks so much!

When Twilight takes a trip to Canterlot to see Cadence's ultrasound, she gets the shock of her life. Celestia has chosen a new personal student. The news sends her into a world of unknown fear and worry, forcing questions into her head. Will she be forgotten, has the distance between her and her teacher become too great, and how can she deal with that fear. With the help of her friends, she will learn a special something about mothers.

Art by post scripting

As Twilight and her friends faced off against Nightmare Moon inside the decrepit castle of the pony sisters deep within the Everfree Forest, The mare in the moon strikes first, defeating the element bearers. In an attempt to finish the job Nightmare freezes in action intent to discover the familiar energy hiding underneath the vale of her first victim. What lies underneath could change the lives of both Nightmare Moon and the pony forever.

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In this Story, Nightmare Moon was not neccassery Evil. Also was Celestia here a thousand years ago not the Pony, as we know her.

I didn't hate Celestia. I really like her! This Story is only an attempt for a Story with a diffrent Past as we know it.

Rated Teen for some......"unprincess" like Words from Nightmare Moon and Celestia, maybe others to^^

New Cover art! Made by happyowl

Twilight Sparkle is at the castle library again doing her normal research. As she finishes her studies for the day, a book with a unique title catches her eye. What will she find in this book, and what will happen after she's read it? Read and find out.
This story takes place before the events of the show. This story was inspired by the picture I found in this link: The Lost Princess
I do not take credit for the picture and thank it's original artist for inspiring this idea.

After helping Spike and Rarity while the little dragon was cursed as a werepony, Princess Luna sets out to do all she can to help the other ponies that embodied the Elements of Harmony. On her journey, she finds friends she didn't realize she had and something more.

The story continues with Hope and Shadows

Don't know what the heck is going on? Then start to story right by going all the way back to the beginning with And Tootsie Flute Makes Three