Diablo Crossover.

The Archangel of Justice destroyed the Worldstone to spare Humanity the corruption Baal infected it with. The force of its death knell shatters Mount Arreat and sends Tyrael hurtling across the endless planes of reality. He falls upon a world untouched by Angel or Demon, far from the sight of the High Heavens. So far, in fact, that he fears he will not be reborn from the Crystal Arch.

Wounded and near death, hope appears in the form of two strange creatures bearing the power of night and day.

Tyrael now faces a time of recovery as his power slowly heals within a body fashioned for him by his saviours. Justice Incarnate tastes for the first time the life of a mortal, and it is a strange, confusing experience .He has been left in the care of one Twilight Sparkle to learn of this world.

After all, where better to find peace and harmony than Ponyville?

Act I - The Root of Evil
Act II - ????????
Act III - ???????
Act IV - ???????

[Cover image used with full permission of the owner. Go on, go have a look at Chagial's stuff.]

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