Celestia is trapped on Earth.
Not as a human. Not as an alicorn. She's a common horse, an Arabian mare, without her magic, voice, knowledge of the language - not even freedom, forced to work at a riding school.

What can a single Arabian mare do to get back to Equestria from this backwater European country? With only the mind of a princess and a pencil in her teeth, Celestia must find a way home.

[Illustrated] [Alternate Earth] (without Bronies)
Rated Teen for language and some scarce suggestive themes.
Proofreading by AlicornPriest

Polish language version

After a tragic accident, a human ends up in Lord Tirek's body, as part of an attempt to reform the villain after his recent escapades. While the hero of our tale is trying to make sense of his new surroundings, the rest of Equestria thinks that the most terrible threat that their world has ever seen is back...
And the powers that be are definitely not happy about it.
New Cover Art By Shadow Bolt

Takes place in an alternate universe where Celestia and Luna used the Elements of Harmony to slay King Sombra.

Celestia and Luna are no more. The sun and moon have collided, and the heavens torn asunder in the aftermath of their final battle. The Elements of Harmony are missing, presumed forever lost. The fiends of Tartarus are on a rampage, and no one can stop them. And to make things perfect, the ruler of the nation of Boardor has decided to invade.
Desperate, Clover the Clever's last living student gathers together 108 virgin mares, in order to perform a ritual that will revive King Sombra. They succeed... kinda.
A human, in King Sombra's body, suddenly finds himself in an Equestria in a downward spiral with a bunch of technicolor ponies begging him to save them. Convinced that he's either dreaming, stoned, or insane, he tries to go along with it as best he can, although the voice in his head, a very angry voice with a hunger for conquest, crystals, slavery, and stairs, isn't doing much to instill confidence in his own sanity...

New Cover Art By Shadow Bolt!

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 )

Semper Pie is one of Equestria's most honored and decorated soldiers. Protector of the innocent, hero of countless battles, champion of all ponykind. Even Shining Armor, ex-Captain of the Royal Guard, and Prince Consort to the Crystal Princess, looks up to this great stallion. Truly one of the best and greatest ponies to have ever served under the Royal Sister's banner.

Still, where did he come from? Where was he born? What has he done? Does he have any family? Why would he suddenly want to come to Ponyville?

And why, for the love of Celestia, does he specifically want to meet with the Element of Laughter herself?

It took many long years and far more defeats than he'd care to admit, but at last—at long last—victory was finally within the great Ahuizotl's reach. Absolutely nothing, not even that meddlesome Daring Do, would be able to stand in his way any longer. Yet even with his arch nemesis facing her inevitable demise and the ultimate power literally in his grasp, he can't shake the feeling that he's forgotten about something.

One tiny, crucial detail. Something very important. As in, 'could easily ruin his plans if not attended to' important.

...

Eh, maybe he just left the oven on again.