This isn't where I belong. I left all this behind years ago, moved on with my life. But a mare from my past brought me back, and now she won't let me go. So I'm stuck here, trying to make the best of it with ponies that don't understand me, don't even like me. But when something moves in the darkness, and when things go wrong in the cold, dead night, they'll turn to me to try to set things right.

Why? Because once a police pony, always a police pony.
~~
This is a spin-off story to 'Why am I Pinkie Pie?!', and will contain spoilers for that story, but it's not necessary to read that story to understand this one.
Cover art by the talented Conicer
Need more Cinnamon Swirl? Merlos the Mad wrote a fanfic of this story!

There is now a side-story: A Hard Day's Nightmare Night

Equestria's history is full of wonders, both magical and mechanical. But only twice has it succeeded in implementing AI.

The latest iteration is an apple farmer whose resurrection is celebrated by everypony except herself. Because really, once every part has been replaced, what is left that can measure a mare?

An entry for the 2023 Sci-Fi Contest, where it nabbed a respectable fourth place. Yay, existential robot ponies!

It's April Fools Day and Twilight Sparkle is weary of the days pranks. Yet, throughout the day, she can't shake that there's a joke she's just not getting.

Featured: 4/2/2023

This story is a sequel to Iron Hearts: Book 4 - Emerald Dawn

An MLP/Warhammer 40K crossover, part 5.

With their plan established and put into motion, the 38th Company begins the long and unwieldy task of planetary defense, fueling the arcane energies that may yet unsteady the Empyrean and spare their fleet from an enemy without number or mercy. The inhabitants of Centaur III and even the abandoned aggressors help where they are able, but as their foes grow in number and destruction spreads across the planet, the war for the Centaur system has become a bloody race against time.
All the while, the grim culture of the Chaos marauders continues to mingle with the enlightened benevolence of their equine allies. Tempers fray and allegiances blur. But the die has been cast: Equestria and the Company will survive together, or be snuffed out together.
And even should they succeed, what future awaits these unlikeliest of friends?
For there is no peace among the stars. Only an eternity of carnage and slaughter, and the laughter of thirsting gods.

ALL THE EXPLOSIONS. JUST, ALL OF THEM.

(Cover art by Ahrimatt)
(This series now has its own TVtropes page!)
(This series is a contestant in the Tournament of Canterlot, a charity event to raise money for Syrian refugees! Go here for details and donations!)

This story is a sequel to Iron Hearts: Book 3 - The Sept Lamman

An MLP/Warhammer 40K crossover, part 4.

The Tau threat has passed. The fleet that once thought to sweep aside the tainted pirates of the 38th Company has fled the system. The Lamman Sept is broken, demoralized, leaderless...
... And victorious.

With Lamman's plan put into motion, an alien horde hurtles through the Warp toward the Centaur system, its soldiers without number and thirsting for violence. Equestria's heroes must find a way to stop them, or the entire planet will be overrun with ease and its inhabitants butchered. While they could afford some pretense of neutrality and disinterest in the fight between the Iron Warriors and the Tau, now it is their world that lay in the crosshairs of the foe. Ponykind will need help to survive, and they look to the forces of Chaos for aid. But is there any hope to be found in the darkness?

EXPLOSIONS ARE IMMINENT.

(Dark humor warning; mild grimdark)
(Cover Art by Ahrimatt)
(This series now has its own TVtropes page!)
(This series is a contestant in the Tournament of Canterlot, a charity event to raise money for Syrian refugees! Go here for details and donations!)

This story is a sequel to Iron Hearts: Book 2 - Ferrous Dominus

An MLP/Warhammer 40K crossover, part 3.

The formal negotiations between Equestria and the Iron Warriors have failed. Yet peace and even cooperation between the harmonious ponies and the corrupted militants blooms in the dark corners of Canterlot and the open streets of Ferrous Dominus. The Elements of Harmony are safe, trade flourishes, and cautious meetings grow into lasting friendships as an unsteady calm descends upon both forces.
Even the Tau threat seems to have mysteriously vanished as the Iron Warriors refuse to assault their hideouts and risk springing the traps of the Fire Caste.
But the Tau have not vanished. The Lamman Sept of the Tau Empire, the Fire Caste's hidden dagger, have come to grips with the slumbering giant looming over their doorstep and have moved forward into the final phases of their plan. Fleets ply the void, hunters stalk the orchards, and in the depths of the badlands a strange device is rapidly assembled for purposes unknown.
The Tau alone know that time is running out, and more than just the fate of Centaur III hangs in the balance.

SIGNIFICANT POSSIBILITY OF EXPLOSIONS.

(Dark humor warning; minor grimdark)
(Cover art by Ahrimatt)
(This series now has its own TVtropes page!)
(This series is a contestant in the Tournament of Canterlot, a charity event to raise money for Syrian refugees! Go here for details and donations!)

This story is a sequel to Iron Hearts: Book 1 - Planetfall

An MLP/Warhammer 40K Crossover, part 2.

Celestia has handed down her order. The Iron Warriors must be defeated and driven from the planet, lest the corrosive grip of Chaos infect their world. With great reluctance, Twilight and Company depart for the Iron Warriors fortress-factory in order to confront the Chaos Warsmith. However, in this mission it is not the might of the enemy that will be their greatest challenge, but their own burgeoning friendships with the admittedly less-than-saintly members of the 38th Company.
At least until the Iron Warriors actually consider them a threat. Then it's totally their military might that will prove to be their greatest challenge.
All the while, the Tau forces lick their wounds and plot their next move. They are far from defeated, and the Iron Warriors have little inkling as to the aliens' true purpose.

MORE EXPLOSIONS!!

(Dark humor warning; minor grimdark)
(Cover art by Nicholas Kay)
(This series now has its own TVtropes page!)
(This series is a contestant in the Tournament of Canterlot, a charity event to raise money for Syrian refugees! Go here for details and donations!)

An MLP/Warhammer 40K Crossover

The Iron Warriors 38th Company has landed in Equestria, entrenching themselves like a barbed hook. They hunt the aliens of the Tau Empire, intent on destruction and pillage.
A small squad is dispatched on a reconnaissance mission, only to find that there is intelligent life on this world besides the feuding space-farers.
Will these improbably adorable and friendly equine aliens turn the damned warriors of Chaos from their blood-soaked path, cleansing them of their dark legacy with the magic of friendship and harmony?

No.
No, that isn't happening.
EXPLOSIONS!!

(Dark humor warning; limited grimdark themes)
(Cover art by Nicholas Kay)
(This series now has its own TVtropes page!)
(This story is a contestant in the Tournament of Canterlot, a charity event to raise money for Syrian refugees! Go here for details and donations!)
(Featured on Equestria Daily 8/20/15 )

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