Ciaphas Cain, Warmaster of Chaos and Age of Iron Crossover. These are various fics that I've crossposted on the CC:WC thread on Spacebattles.com, posted here for your entertainment and amusement.

Caring for an Alicorn can be hard. Especially when you’re in an alien hive, you’re a xenomorph that chewed its way out of said Alicorn’s chest a few weeks ago, and the Alicorn you’re trying to care for, A.K.A. Twilight Sparkle, is convinced you do not have her best interests at heart, despite all your attempts to prove otherwise.

MLP:FiM/Alien Quadrilogy crossover. Gore tag is for implied incidents in the past. Nothing graphic actually occurs during the events of the fic.

King Sombra survived the power of the Crystal Heart, and for a moment, it seemed as if his victory was assured.

But then the undead warlock Richard shows up. Turns out, he's been talking to the Crystal Ponies, hearing tales of what they've suffered at Sombra's hands. And surprisingly enough, he is not a fan of what Sombra has been up to.

Needless to say, Sombra's day has just taken a turn for the worse to end all turns for the worse.

A short, silly crossover between My Little Pony: Friendship is Magic and Looking For Group. Dark tag is for Black Comedy and Richard being... well, actually, he's really being a lot more morally upright than he usually is in the original webcomic. Probably has something to do with the fact that his preferred battlecry is "for pony". Anyway, even though the target of Richard's depredations may be fully deserving of it (this time, at least), there are still implications of an I Have No Mouth Yet I Must Scream-esque fate, so the dark tag stays in place.

So... my name is Ciaphas Cain, and I am—or, at least, I was—a newly-minted Commissar fresh out of the Schola Progenium. By some horrid twist of fate, I got assigned to the Valhallan 18th and its infamous Commander, which has just been sent to a newly discovered backwater garden world to dispose of its oddly horse-like xeno population.

The next thing I know, I'm stranded on the planet in an alien body, the Xenos’ leader is in a coma for the foreseeable future, and her subjects—despite knowing full well that I was once a member of the same group of Imperials who’d struck her down—have shoved me onto her now-vacant throne for reasons having to do with the fact that my new body has wings and a horn. And I'm apparently a psyker now thanks to that horn, and a stupidly powerful one at that. Oh, and have I mentioned that these xenos expect me to somehow lead them to victory against the trigger-happy Inquisitor that seeks to wipe them off the face of the galaxy with nothing but my savviness, a cunning mind, a silver tongue, the resources of a race completely oblivious to the grim darkness of the far future, and the magical power of peace, joy, rainbows, and orbital friendship lasers? I don't think I had.

Brace yourselves; things somehow manage to get even wackier from there.

This is heavily inspired by Ciaphas Cain: Warmaster of Chaos, and as a result it does not take itself too seriously. If you want a grimdark brutalization fic in which the ponies get slammed with the horror of war, prepare to be disappointed.

So, Twily, seems you've just been visited. By a bunch of murderous alien monstrosities that call a moon-sized biomechanical sphere home. Who've abducted you and want to do some truly horrific things to you. But don't worry! This inappropriately upbeat, inexplicably specific, admittedly somewhat lemony guide is here to guide you through every nightmarish, horror-laden step of the way!

Just a quick note before we get into the story; if you’re gonna downvote this, I’d appreciate a comment explaining why you did so, preferably something a little more constructive than just “this story sucks” with no further elaboration. Thank you.