Iteration 1 (no longer exists outside of a single google doc and the wayback machine; complete)
Iteration 2 (the rewritten version)
Iteration 3 (mostly identical to Iteration 2 with a few changes, mostly where the in-between scenes are, a little bit extra for the Pony of Shadows to do, and the removal of some bad jokes and a lot of profanity)

Currently in Iteration 2.1, but only up to Seven Seals. Everything else is still Iteration 2

Everything Involved: Loomis Comics, My Little Pony G4 (Movie and FiM), SCP Foundation, the Holy Bible (the Book of Genesis), Sonic the Hedgehog, The Flash (2014), Skylanders Academy, Among Us, Team Fortress 2, Kirby, and Undertale (the last four are debatable)

Light violence (like the kind of thing you'd see in an animated movie) should be fine without this tag.

*Laughs in Green Snake*

Anyway, time for the real description.

The SCP Foundation has been working to keep the anomalous under wraps for centuries. A single discovery may lead to their destruction.

The Crown Court has been peaceful since the Great War many years ago. The peace they have enjoyed is about to break.

Grogar escaped from his prison during Cozy Glow’s brief reign over Equestria, but before he could launch his assault, he was sent to hell. Now, with a new ally, he escapes, and prepares to reconquer Equestria.

Their destinies will collide, worlds will die, and the multiverse will never be the same.

Death tag because in chapter 7 alone I killed 5 billion people. The death count otherwise is in the triple digits range.
Violence and gore mostly in the final chapter
Profanity because... why not
Chessmaster is the final chapter packed to the brim with "comedy". From Temple Peak onward, the subplots have very little comedy while the main plot keeps its "comedy" all the way until Destiny (does not apply to Iteration 3)

Totally real reviews:

Comedy is trash, doesn't represent the struggles of trans people in Ukraine, barely even has My Little Pony in it. Then again, you perfectly encapsulated my sense of humor.
-P.R.U.A.L.C.S.
★★★★☆

Literally just trash. Would give zero stars if I could.
-ShadeFire
★☆☆☆☆

WHAT A MASTERPIECE!
-TotallyNotNightFlame123
★★★★★

How do I rate? Anyway 11/10, NightFlame for King of the Labyrinth
-King Minos
☆☆☆☆☆ (rating pending)

I think I shat myself
-Thomas
★★★★☆

Not nearly enough adult jokes, but have a five star anyway.
-Loomis
★★★★★

Please stop, we all know you're just wanking your OCs at this point
-Spencer
★☆☆☆☆

I think I broke something, how do I fix it?
-The Hackerman
★☆★☆★

I loved this
Edit: I can edit my review but how do I edit my rating
-aaabaaajss
★☆☆☆☆

After a great calamity, many worlds are merged. This is a time for heros!..but also villains. One boy must cast off the shackles of normality, build his TRUE family, become a man, save the world. But above all...he must SECURE. CONTAIN. PROTECT.
MASSIVE CROSSOVER! Wendy/Dipper, Dipper clone/Pacifica, dipper pony clone/Twilight Sparkle Ronnie/Lincoln/Six.

MERRY CHRISTMAS!

Major AU! What if it was not just Sabo, Luffy and Ace kicking it at the Dawn islands? What if a Twilight Sparkle was among them from the beginning? And what if a certain RAINBOOM happened the day of the Grey Terminal fire?

SPOILER! There will be elements of harmony, but it WON'T be Twilight and her friends...you'll never guess who!

Blair Witch Project/ SCP You Do Not Recognize the Bodies in the Water MLP crossover.
Rarity, Rainbow Dash, and Applejack go on their yearly camping trip with their sisters.
After some spooky stories from Applejack, and then Rainbow Dash, things start to get a bit... wierd....

Doctor Whooves A.K.A. Time Turner A.K.A. Doctor has been in Equestria for a while. For once in his long long life he found a place that didn't resort to mindless wars and fighting and found peace. But he couldn't shake his paranoia that something might happen. Despite nothing from his own past coming to ruin Equestria other realities might. Teaming up with Derpy Hooves, the Doctor sets out to fix the alternate timelines so that they don't influence his Equestria.

Luna makes her way to her sister's cambers while fighting off creatures from the deepest depths of Taurturs, just to know what went so wrong in just two hours.

My mediocre submission for the funny bunny . 1000 words only contest

Its Halloween at the SCP foundation again, and nightmare night in Equestria.SCP 106 is bored yet again, however, he has just the thing to cure his boredom, and this is sure to be a night the foals of equestria will never forget...

'Cleaved' AU! Mina's defeated, Star and Marco are reunited, happily ever after, right?...yeah, not so much.Without realizing it, Star has messed up the wrong organizations 'backyard' and their going to 'teach' her why she just made a BIG mistake...

Star messed up BIG time and it's going to affect the lives of COUNTLESS worlds...