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

The War of the Witches? Ever since you began visiting me here in my garden, my newest student, your inquiries have all revolved around that ancient conflict. I will admit, I wish you would ask me about something else. No? Very well. You have selected the subject, but this evening I shall choose the setting, as I believe there is something I need to say.

Yes, something I need to say indeed…

A thousand years is quite the generation gap, so Princess Luna decides she has to get with the times. However, this isn't quite as easy as she thinks it will be...

The Lone Wanderer has been known as the man who shouldered the nightmares of every man, woman and child in the wasteland, so that they may live. But when the Wanderer was once again abducted by aliens, he found himself falling, quite literally, into a whole new wonderous world, untouched by the horrors of nuclear devastation.

He has been facing other people's nightmares constantly for almost a decade, it was high time he was allowed to wake up.

Meanwhile, the ponies of Equestria are baffled by a strange object that fell from the sky.

Fallout/FIM crossover. HiE. T for violence and some language.

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King Sombra’s dark influence was obliterated by the Crystal Heart, and the villain is well and truly dead. But when he attempts to steal the afterlife of an innocent victim, a human spirit is left hurtling towards Equestria, where this unfortunate soul is revived into the only vessel available: the reconstituted body of King Sombra himself.

Thus, a cheerfully oblivious alien is crammed into the form of the most evil and malicious being Equestria has ever known. Not that Shining Armor and Cadence know this, of course. As far as they are concerned, the King is back and he’s lost his fricking mind.

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Discord has been turned to stone by the power of the Elements of Harmony, but his consciousness has been left uneffected. Now powerless, he can only observe the events around him and think on his past life.

(Want more Discord? This story has a sequel! Diary of a Pliant Tyrant)

This story is a sequel to Diary of a Silent Tyrant

It's funny what an idle slip of the tongue can lead to. When Discord makes an off-hand comment to Fluttershy about the mental diary he kept when encased in stone, she begs him to continue it. She says it will be "therapeutic", but he's sure it'll be a real bore. But who can resist those puppy-dog eyes and a bribe of fresh cookies? Grudgingly, he takes up a pencil to document his thoughts and experiences in his new life. A life among his old enemies. A life he never wanted.

Cover Image by Grievousfan who makes awesome art!

As a stranger in a strange land, sometimes you need to get a different perspective to see how you might fit in. Jeremy gets his chance to see Equestria from the bottom up when he gets in trouble with the law. Ponies have such a happy, peaceful society that it's easy to forget that perfection doesn't exist, and there's always going to be misfits and the disenfranchised.

“It is said that no one truly knows a nation until one has been inside its jails. A nation should not be judged by how it treats its highest citizens, but its lowest ones.”
― Nelson Mandela

Tensions grow hotter in the mining town of Farrington after the events of one disastrous night. The fallout from this blaze will test many citizens' relationships in fire. Some will falter, but some may perservere.

Before any repairing can begin, ponies—and one griffin—will have to take stock of their pasts, or else their futures may end up strangled by their scars.

Note: This is a sequel to Summer Days. I strongly encourage reading that story first.

Special thanks to Gaiascope for this awesome cover!

In the heat of the moment, some ponies have a habit of letting things out. Sometimes they are minor things that most just shrug off and forget about in a matter of milliseconds. Sometimes they are things that, once revealed, shake the very foundation of their existence.

Rarity's latest revelation falls into the latter.