This story is a sequel to The Shadow of the Mare

After the events of The Shadow of the Mare, Loop D'Loop takes up the cape and cowl of Mare Do Well in a bid to get more love and affection from the ponies around her. But a few careless mistakes lead to events spiraling out of control, and it's only a matter of time before she's revealed as the changeling she really is.

A journal was found. Old and weathered with years untold. The first entry was dated yesterday:

My name is Twilight Sparkle, and for the last 33 days I've been stuck in a time-loop, repeating the 23^rd of March, 2 A.R. It is still unknown how the loop started, nor how I can end it. All I can say with any amount of certainty is that time for the rest of the world resets every night, and every morning I wake up it is the morning of the 23^rd.

Now with a reading by ObabScribbler. Link!

One hundred and thirteen people find themselves standing in a dark, round room. They are neither living, nor dead. They will be offered a single choice, and they will be asked only once.

This is a story set in Iceman's Friendship Is Optimal universe, but knowledge of that work is not needed to understand this tale.

Humans.

Truth or myth? Ancient lost civilization or just an old pony's tale?

No pony has ever seen one, and most haven't even heard of them. But Lyra knows that these wonderful creatures are more than just old legends, and she's going to find out... and possibly drive her roommate insane in the process.

Hanna, the CEO of Hofvarpnir Studios, just won the contract to write the official My Little Pony MMO. Hanna has built an A.I. Princess Celestia and given her one basic drive: to satisfy everybody's values through friendship and ponies. Princess Celestia will satisfy your values through friendship and ponies, and it will be completely consensual.

An argument and a car crash leave one of the sirens--Adagio, Sonata, and Aria--dead. They know this because Death itself has shown up to chat with them and to ensnare Adagio into a game of wits with the very lives of her companions at stake. Adagio doesn't want anyone to die, but she's not so happy with the way they've been arguing so much lately either...

An EQG story. Absolutely no connection to The Years of Ar and S.

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