Here's a crossover shipfic that I had an idea for:

Maud Pie x Eeyore

That is all.

One Step (down) At A Time
Tags: Slice of Life? Random? Comedy? I honestly don't know.
Characters: Celestia, Luna

Let's face it: Celestia and Luna are pretty much gods. Er, goddesses. And while they're given a lot of fear and respect, and their names are sometimes used as oaths, there doesn't seem to be any sort of official religion around them. Heck, they don't even have particularly high titles, like Queen or Matriarch or anything. Why?

Because since the founding of Equestria Celestia and Luna have been working on getting less reverence from their little ponies.

When they saved the world from Discord, they were revered as deities.
After the unification of the three tribes, they were hailed as queens.
Since the rise and fall of Nightmare Moon, Celestia has insisted on being a princess.
In the next few generations, she plans on transitioning to an elected position (Voice of the Stable or some such)

So, wait, what's the actual story?
I... honestly don't know. Maybe have a discussion between Luna and Celestia on the next steps of looking like fallible, approachable ponies?

"Alright, we've got... 'be spotted reading a trashy romance', 'getting caught up in a recent and inane fad' and... ooh, 'eat something messily and go around with something on your face until somepony points it out'! I call dibs on that one!"
"Aww~! Tia, you always grab the fun ones!" Luna said with a pout.

3381769
I'd like to claim for my writing during Oneshotober.
The idea of Spike being Starswirl is to awesome to pass up!

3354144
Thank you for having this idea! It would be awesome for Oneshotober!
Poor Tia getting Sunstroke. *snickers*

3342801
I love this idea and would love to make it into a oneshot as one of my stories for Oneshotober!
I'm not sure if i'd have Luna fake her banishment or not. gotta figure that out.

3516933
Yes please, I'm a vocabulary nut. This would be perfect for one of my one shots during Oneshotober!

3621572
3621575
Go for it! I look forward to seeing how they turn out.

I wouldn't worry too much about having Luna fake the banishment. That's more of a set-up for an on-going adventure in the past and not really suited for a one-shot. That's my thought, anyway.

- Don't have a title, hope someone make it interesting
- Characters: Sunset Shimmer, Mane Six, OC's
-Tags: Slice of Life, Human (of course), Sad (probably)

"Sunset manage to be friends with the HuMane 5, but she doesn't trust them yet enough to tell them about her life back in Equestria; and things got more complicated when some people of her past (better said, versions of her past) show up and bring happy (and sad) memories that she burried a long time ago"

I have in mind the next points:
-Human Sunset died as a little kid; years ago before Pony Sunset crossed the portal.
-As a cosmic thingy, Pony Sunset's parents died around the same time that Human Sunset died, and in similar circumstances.
-You may know whose people are gonna appear in Sunset's life.

At first, Sunset will encounter by accident with this human version of his dad, Morning Star, and even if he doesn't recognise her (after all, human Sunset died so young) Morning Star could not help but feel a conection with Sunset (she will use a fake name around him). Sunset tries to avoid him but as matter of destiny they encounter each time.

Sunset already knew about the death of her mirror version, once she noticed all those mirror versions and learned to use the technology of this world, she found out. Also, she also knew time ago that those mirror versions of her parents started to grow apart of each other and divorced.

Morning Star works in the Astronomy department at the Museum of Canterlot City.

Summer Glow, Sunset's mother, is a famous writer of sci-fi novels.

If these background information of the characters does not work, feel free to change it.

Really convoluted time travel plot.
[Romance, Random, adventure, alternate universe]
[CMC, Twilight, Rarity, Flash Sentry, Diamond Tiara]

You know that one OC that looks like Scootaloo but is actually Flash Sentry and Twilight's daughter in the future?

Well what if that is Scootaloo? She is actually Twilight and Flash Sentry's kid from the future trying to prevent her own timeline from unraveling.

Sweetie Belle is actually Twilight and Rarity's kid from the future as well, who is pretending to be her aunt Sweetie Belle, who is actually in Fillydelphia in a boarding school. She comes from a different version of the future, where Twilight and Rarity get married and magic lesbian horse stuff later, has Sweetie Belle.

Obviously the two are at odds with each other. When Apple Bloom finds out, she tries to help with a third option where both of them are born, but that gets more convoluted when they realize it's one or the other, and when it happens, they not-happened one disappears into thin air, Ala Back to the Future.

Even more complicated is when it is revealed to Apple Bloom that Diamond Tiara is also from the future, the daughter of Cadence and Shining Armor. She's secretly an alicorn and that's why she's all high and mighty, she's an alicorn time traveler from the future. Yes, mention that Diamond Tiara is cousins with Sweetie Belle and Scootaloo.

Since this is a light-hearted story, come up with a way to allow both Sweetie Belle and Scootaloo to exist. Please don't make this sad, dark, or tragedy. Make it so one of the timelines becomes the true timeline, while the not-happened one to disappear, but they are able to save the time traveler. Diamond Tiara doesn't care which one, because she exists in both futures.

Find a good way for the time traveler who lost her future and family to come to terms with it, or come up with a way to visit her family (multiverse theory, for example).

Seriously, the first three or so chapters should be the Whaaaat? reaction of Apple Bloom to the reveals.

Rarity becomes a bird.

Rarity blows up for no reason, and becomes a bird. A sparrow to be precise.

Changeling Call Center.

Kinda based on the anime Trigun. After Discord's release, an Equestrian insurance agency sends a pony to follow him around and befriend him so the agency can predict and possibly ameliorate Discord-related insurance claims, and not go out of business. :-)

3332839

Hmm... If nobody else asked, may I take up the challenge of using that idea? If yes, can I add in and change some aspects to but not majorly big ones, if it's ok I use that idea. I'm a pretty decent writer although I have no published ones on this site yet really. So, may I claim that idea?

3770933 Go for it! I'd love to see what you'll do with it :)

3771317

Alrighty then!

I promise I won't fail you

XD

Princess Diamond Tiara
[Comedy Random, ]
[CMC? Celestia? Luna? Diamond Tiara, Silver Spoon]

This came about from a comment on a story I posted. Basically, by whatever machinations you want to use, Diamond Tiara becomes the sole ruler of Equestria and proceeds to rule with an iron hoof. (Maybe there's some obscure law she exploits, maybe her tiara is actually an ancient artifact that certifies whoever wears it is the sole monarch of the realm.)

I can see a couple of ways to go about with this Either you focus on Diamond Tiara as ruler, (is a she a tyrant? or maybe she finds the petty bulls**t that rulers have to endure intolerable.) Or you focus on the CMC and their quest to depose her. I suppose it could be a serious fic but I think it works better as a comedy.

3630843
I'm claiming this.
Edit: Someone else can claim this.

3477110 I will claim this idea. I should have this alive by the beginning of next month if all things don't start going against me or something.

3774142 You know I was working on something like that. I should also be out with something like this soon or in the coming months at least :3

3790069

I wish you best! I highly recommend watching the episode if you have't already.

3790078 Oh, I most certainly remember that episode. However I'll just watch it again for safe measures. :3

3668467 "Anonymous Changelings" self-help group

Title: The Princess and the Coma Patient
Or: The Princess and the Dreamer
Tags: Adventure, (Romance?)

Princess Luna has an unusual encounter while dream-walking.

Luna finds herself in the middle of an incredibly elaborate dream world wherein <insert name here> has to overcome some great obstacle manifesting some sort of inner fear in order to wake up.

And for some reason, he/she doesn't want to tell Luna what it is.

Maybe Luna can't wake him/her up, but at least can take them into other ponies dreams and reconnect with friends and loved ones . . .

EDIT: Seems somepony over on the [url= https://www.reddit.com/r/mlpwritingprompts/comments/2padrj/princess_luna_visits_the_dreams_of_a_comapatient/]"MLP writing prompts"-reddit group has taken this one on. A short-story is posted in the comments there.
No fimfiction-link though.

Twilight Sparkle is an award winning home schooled antisocial online college student that's only 16 years old. However, Despite Twilight's obsessive study habits, she always makes time to read the morning paper. Or as she calls it, "indirect socializing". One day, Twilight comes across a strange article that talks about an infamous criminal that has escaped prison and gone missing. She doesn't think much about it until Spike comes home from school that day and talks about his new vice Principle. Strangely enough, she matches the description of the escaped convict. However, when she confirms this herself the next day, the police refuse to believe her and Twilight decides to take things into her own hands. During her investigation, Twilight discovers that absolutely no one in the school realizes that a criminal is in their midst, and no one questions it. No one even interacts with her except a few strange girls. Can Twilight play nice with them long enough to expose the supposed "Vice Principle."

Yup, if your smart, than you've realized that this is a humanized FiM rewrite, completely magic free. This is something else that I want to see written. I'm sending this out as a challenge to any write that can make this happen. You need to follow the general (loosely) plot of each episode and write out the main series as it would happen in a humanized environment. I'm even thinking of doing it myself this time, but it's still up for grabs.

Of course if this has already been done feel free to link me the story. Inspired by Thelivingmachine's art gallary

Title: "Apple-Swap" // No good title yet.
Characters: Granny Smith, Applejack, Mane Six
Tags: Comedy, adventure/slice of life(?)

Applejack and Granny Smith switched bodies.

Granny's making the most of it – but Applejack isn't having any of that “Freaky Friday” business.

She's heading straight to Twilight's to get things fixed.

And things might have ended there – if it wasn't for an urgent letter from Princess Celestia requiring the six defenders of Equestria to once again defeat another ancient evil...

Twilight will have to find a solution while on the move. Looks like Granny Smith is coming along for the ride.

Potential subplots include:

1) A young Granny Smith interacts with the rest of the mane six. (I think that'd be rather rare.)

2) While Granny Smith is reliving her glory-days, Applejack contemplates her life, forced to confront the somber fact that, one day, she won't be able to buck apples or do rodeos anymore.

3) Pre-confession AppleDash-ship. Made especially awkward by Applejack's wrinkled appearance. In the very end, Rainbow Dash finally overcomes her inner struggles, confesses her feelings, and shares a passionate kiss with... Granny Smith. Because they'd just switched back.

4) Applebloom and Big Mac also switched bodies.

5) The returning ancient evil turns out to be... King Sombra! And this time, he has taken over... Appleloosa! Granny Smith does not approve of this.

6) A stallion falls head over hooves for the “beautiful and full of life ” Granny Smith. Awwwwkward.

Title: "Special Eyes"
Characters: Derpy, Snowdrop
Tags: Slice of Life, D'AWWW

Derpy helps Snowdrop overcome her self-confidence issues.

On her travels with the Doctor, Derpy has a chance encounter with a young, blind pegasus-filly bemoaning her "useless eyes".

Twist-reveal at the end:
Snowdrop is Derpy's ancestor, which means she grew up to be a happy mother and raise a family.

Possible hints at this throughout the story:
Snowdrop initially mistakes Derpy's distinct wing-flaps for those of her mother.
Derpy/Ditzy off-hoofedly mentions being named after her "great-great-grandmother or something", and the reveal is delivered in the epilogue where Snowdrop names her first-born foal.

There In Enough Time
Tags: ...Whatever works for you.

Like many stories before this one, this has Minuette as a time-traveler. Basically, either she overhears ponies remembering weird things that could only be explained in-universe by time travel, and she arranges for those things to be true.

For example:
We know from Cheese's flashback (depicting a post-Rainboom event, specifically, Pinkie's party in Ponyville) that several background characters, including Minuette herself, are about the same age as the Mane 6. However, a few of those fillies were adults in at least one pre-Rainboom events, i.e., the Summer Sun Celebration that inspired Twilight to study magic as intensely as she did, and at least one event occurring shortly after the Rainboom, i.e., Rarity's play.

Your Job:
Figure out who all this entails. I know Derpy, Bon Bon, and Lyra will be, besides Minuette herself. (Filly Twilight even passes between Lyra and another pony!)

If you're going to object to my idea on the basis that "it's just an error; they just threw ponies in without regard for things like that", then... don't write it, I guess. But one of our most beloved background ponies was born of an animation error, so I don't think there's anything wrong with doing this.

A colt (or filly, whatever) has recently gotten his cutie mark. Then his family's house burns down and he gets burned really badly. The doctors say they can get him back to normal, but at the expense of his cutie mark.
I'm not really good at writing sad fics, and no matter where you take this it seems like it'll end up there.

Angelarchy
Fluttershy leaves to Canterlot for a week. All of the animals are in her cottage without a clear leader. Chaos ensues.
There would be a dynasty, and the French Revolution, and Angel would be a dictator for a bit, and some stuff from the Revolutionary War.

After the events of Lesson Zero, Celestial returns to an evening meal to discuss the events with Luna, who is having difficulty adjusting to life in a modern Equestria. The focus of Twilight's problems, Smarty Pants, reminds Celestial of a keepsake she held onto to remember her banished sister; Luna's treasured doll, Doodles. A slice of life story about keeping alive the memory of those we love, no matter how far away or how long they're gone.

This seems as if it must have been done already, but I can't find it if so:

Sarah Jessica Parker winds up in Equestria, untransformed.
Nopony notices anything out of the ordinary.

Alt: She's an Equestrian trying to fit in in our dimension.

Time and Tiara

“When I was little, ponies didn’t come that purdy.”
—Granny Smith, referring to Diamond Tiara and Silver Spoon, S2E12 "Family Appreciation Day"

Diamond Tiara is at ground zero for some manner of magical mishap. When she comes to, she finds herself in an empty field. A blank flank filly finds her, and Tiara grudgingly accepts her hospitality, such as it is. Soon enough, Tiara realizes she's gone back in time, and that if she isn't careful, she could undo the founding of Ponyville, and thus her own existence. Can she keep herself from causing a somepony-else's-grandmother paradox? And why does that filly keep staring at her?

Bubble and Squeak
Tags: Slice of Life, anything else you like
Characters: Derpy, Dinky, Luna (optional)

Derpy is a bat-pony.

She wears contacts to disguise her eyes, trims her ear tufts, and wears bulky feather-covers over her real wings. She's constantly crashing into things because her eyes are naturally weak and she's afraid to use her sonar. Her ditziness is because she's not getting enough sleep and caffeine can only do so much. Her clumsiness is at least partially due to the wing-covers... like wearing thick gloves all the time, it messes with her fine dexterity.

Why hide it?
Bat-ponies were always closely associated with Luna, and even more so with Nightmare Moon. Derpy made the choice to be pitied as a klutz rather than shunned as a bat-pony.

Why keep hiding it?
Sure, Luna returned and was redeemed, and bat-ponies are being reintegrated into Equestrian society, but... well, 1000 years of bias are hard to overcome. Also, she already has a life she's comfortable with in Ponyville, and dropping the disguise would change that. Better, worse, change is still change, and change is scary.

More importantly though, is Dinky. Her mom being known as the town klutz is one thing... but if her mom was known as a bat-pony, who'd been secretly living in Ponyville all this time? No, no, Derpy couldn't do that to her filly.

Where to go with this?
1) do a straight slice-of-life from Derpy's point of view, showing how she gets by while hiding her true self.

2) have her sit Dinky down for a mother-daughter talk. Maybe start off making it look like it's going to be "THE Talk" ("You're getting older, so you're going to start growing hair in strange, new places... like the tips of your ears.") only for Derpy to explain her heritage and what it means for Dinky. ("You're a unicorn, so you have nothing to hide, but one day you might want foals of your own...")

3) Something goes wrong and her disguise is ruined. Derpy flees in a panic, only for her friends to track her down and reassure her that they still like her. Acceptance, friendship, d'awwww-s all around.

The story of Donut Steel, a humble manufacturer of toroidal gas storage tanks.

Pinkie Pie has to get her helium from somewhere...

Title: “Diagnosis: Immortality”
Characters: Twilight Sparkle, others

On a routine checkup, Twilight Sparkle is diagnosed with immortality.

“Doctor, how long do I have?”

“I can't give you an exact number, Ms. Sparkle. But by my estimate... you have a few thousand years to live.”

“Oh no! Isn't there anything you can do?”

“I'm afraid there is no treatment. It is very common among alicorns. Even so, cases are rare, and research in the past thousand years hasn't made much progress.”

How will Twilight Sparkle handle her burden? How will her friends react? How does Celestia deal living with her immortality?

Can Discord – also a victim of immortality – be persuaded to stop making inappropriate jokes about the subject?

... A Crack-fic comedy about Twilight sulking about immortality, treating it like an illness.

Party Favor with his madhouse balloon crafting skills inserted into prior episodes of FiM, easily resolving all the mane six's problems in sheer minutes.

Title: "Escapism"
Characters: Original Characters

A father searches for his little filly, who ran away from home to live in an enchanted comic.

The twist:

"Come back to reality? Come back to REALITY?!" she yelled back at him. "You always tell me stories of how you used to be a 'human' from another dimension, and how Equestria was YOUR dream-world! YOU got to live in YOUR dream-world, dad! Why can't you let me live in mine?"

The story leading up to the twist is sprinkled with short bursts of flashbacks to everyday household life, subtly hinting at but never quite revealing the "Brony went to Equestria, turned into a pony ... and now it's 20 years later, and it's life as usual"-setup.

- dealing with a halfway-decent job ("Shockingly, the skills he had learned had turned out not to be high in demand in Ponyville.")
- little father-daugher moments ("You're my Little Pony," he lovingly fluffed up her mane. "Daaaaaaaaad, I'm not little anymore!")
- family discussions at the dinner-table ("Please, at least look at the prospects I gave you. I'm a pegasus, you're a pegasus, our daughter is a pegasus. Why can't we move to Cloudsdale? I know you love Ponyville, but our daughter needs to go to a proper Flight School.")
- lampshading the whole "Brony interacting with mane six / popular background ponies" shtick ("Oh. It's you again." and/or getting sternly glared at by a Ponyville-guard)

Title: "Life without Ponies"
Characters: Spike, Cranky Doodle Donkey, Zecora, cows/sheep

Every single pony in Equestria has vanished over night. It is now up to Spike, Cranky Doodle Donkey, and Zecora to save the day.

... And then the Diamond Dogs showed up.

Alternate setup:

It is now up to Spike, Cranky Doodle Donkey, and Mootilda , one of the town's cows, to save the day. Zecora, meanwhile, is bed-ridden with a sickness, and they need to travel to get medication from another town or a city.

Obviously inspired by this and the accompaning MLP promo-video.

Some more thoughts on the scenario;

The larger cities would probably still have the largest population of non-ponies. Especially Canterlot, there would be a lot of foreign ambassadors and staff in the castle.

It wouldn't quite be a "zombie-apocalypse", but society would suddenly lack vital components and institutions (mail delivery, train-service) to function, at least for a significant length of time. Plus, other nations might decide this to be a good time to strike, loot resources, or claim territory for themselves.

Not to mention there would be nopony to control the weather besides maybe a few griffons, and nopony to tend the crops. Then again, there would still be plenty of non-perishable foods, and a lot less mouths to feed with all the ponies gone. ...Oh yeah, and there's that whole "sun and moon" thing.

This idea struck me today, and I have far too much on my plate to do anything with it.

The Royal Flying Doctor Service.

Based on the Australian organisation of the same name. Remote areas of Equestria have their medical needs covered by doctors that are flown in on wagons pulled by Pegasus.

While an author could ponify most aspects of the RFDS, the biggest hurdle would be communication devices. Easy if you decide to use radio, or a magical equivalent. More difficult if you stick to canon levels of technology.

Is anyone here old enough to remember the old Flying Doctor TV show? Basically that, but with ponies.

Could be fun for someone with more time than me.

Title: The Definition of a Pet
Alternate Title: What's in a pet?
Characters: Mane Six, Fluttershy

On their way back from one of their "cutie map"-trips, the mane six come across a dragon. A dragon, that keeps a pony as a pet.

Everypony in the group is outraged, and immediately make plans to barge in, horns blazing, and free the pony.

The only one who sees things differently... is Fluttershy.

She is the only one who stops to observe the interactions between caretaker and pet.

It seems that to her, the term "pet" has a very different meaning than to her friends.

(Keep in mind that in Equestria, animal intelligence far exceeds that of their equivalent on Earth, taking Angel Bunny as an example. Then, what does it mean for a pony to hold an intelligent being as a "pet"?)

Some of the mirror pool evaporates through a hole in the ceiling of the underground, turns into cloud then eventually rains on the populace. The effect is some ponies (or other beings) are cloned unpredictably.

4305802

Evaporate the Mirror-Pool, you say?

Oooooooooooh, that reminds me of this picture: [link]

...and this old comment:
"Watch out! It's raining mares!"

4306110 With as many Raritys as there are raindrops, imagine the earth-shattering Wahaha if they were complimented!

Title: "(Not) Without a Fight" (or something, no good title yet)
Tags: Alternate Universe, (Sad), (Slice...ish?)

Celestia has prepared herself. As prophesied, Nightmare Moon returns from her 1000 year-banishment, appearing right before her... and immediately keels over, unconscious.

Fighting Celestia? Taking over the world? No.

Nightmare Moon just barely survived her 1000-year exile. She is weak.

Imagine Celestia's reaction here. She steeled herself to face down Nightmare Moon... but she didn't expect this.

Now, she is too afraid to use the Elements on Nightmare Moon for fear of what it would do to Luna.

So instead, she sits at the recovering Nightmare's bedside... and talks to her. Maybe she can reach Luna this way?

EDIT: Idea was taken, and a short-story was published here.
Though the prompt was received through the MLP writing prompts reddit group, instead of through the idea exchange.

I'll contact the author and ask if they'll want to have their story added to the group shortly, however I have some preparations to make first...

EDIT March 5th, 2018:

Published and added to group:

EA Fragile Nightmare

• MLP: FiM
• Drama
• Sad

“On the longest day of the thousandth year, the stars will aid in her escape.” Celestia was prepared to face Nightmare Moon in battle. What she wasn't prepared for was to face her in a hospital bed.

• Alt. Universe
• Twilight
• Celestia
• Nightmare Moon

Ultra-the-HedgeToaster · 3.7k words  ·  903  13 · 15k views

4324224 This story starts out in a similar fashion, you may enjoy it.

4324857
Uhh... I haven't actually read it, but just from the story description I can see it would be quite different from the scenario I was thinking of.

I'd imagine Celestia would be in quite a dilema here. Nightmare Moon both is what Luna became, and the monster that took her away from Celestia.

And now she's terribly sick and weak - but still very much not reformed. And Celestia still wants Luna back.

"It would be so much easier to face Nightmare Moon in battle than in a hospital bed," Celestia thought.

Thanks for the suggestion anyway.

4324224 Thanks for the reference to this group! I added my story, and I think I'll look around a bit for more prompts...

The Sirensverse
Tags: AU,

We have the Lunaverse, where TIa and Luna swapped places and Trixie is Luna's student, we have the Rainbowverse, where RD is Celestia's student, and we have the Manehattenverse, where Twilight was sent to The Big Horse Apple and made friends with locals there.

So... How about an AU set up where the Sirens Adagio Dazzle, Aria Blaze, and Sonata Dusk are the EoH?

Granted it would take some AU hoop-jumping to pull off. Here's one potential set up, although the author is free to come up with something that makes more sense to them:

Long ago, in Ancient Equestria: I Starswirl the Bearded, Master of Magic, worked to unite the tribes into a single nation of Harmony. However, three beautiful sirens, wielding the magic of chaos-spreading song, came forth to oppose me.

Before their final victory, I tricked them into giving up their voices, and then tore open a portal in time, where Harmony is Law! Now the sirens seek to reclaim their gift of song. But in order to do that, they must learn the secrets of Harmony, and the Magic of Friendship, with the help of Ponykind that has arisen in the far future...

So, Starswirl's spell managed to rewire the Sirens singing and magic to only work when spreading Harmony, Friendship, and general Uplifting Feelings, and they've been sent to modern Equestria, a few years before NMM's return.

Perhaps Starswirl mentioned the sirens coming, hinting that they would "Be of assistance." Depending on how AU the author wants, she can try and hedge her EoH-Bearer bets and attach Sunset Shimmer, who hasn't left for the Humanverse (yet) as the Sirens' minder while she trains Twilight.

So we have the three sirens having to relearn how to sing again via friendship (character development! Yay!), and Shimmy may provide more story fun due to feeling abandoned for Tia's newest protégé, Twilight.

Nightmare Moon would be a good Big Finale, though if the plot is carried on to Discord, we could see the Sirens face the temptation of regaining their "True Powers."

However, this fic would require access to poetry/lyric-writing skills.

When Starswirl opened the portal to banish the Sirens to the human world, a toddler wandered through to Equestria.

à la Baby's Day Out (1994).

(From my ideas document; hopefully I haven't posted this before.)

Title: <No title yet. Insert something fancy here relating to a travel agency or trade business>
Tags: Slice of Life, Alternate Universe
Characters: Various

Two parallel Equestrias open trade and travel with each other for the general public.

Write a 'slice of life'-piece on the everyday consequences of two parallel universes interacting with each other.
No world-ending threats (e.g. no 'Equestria A must save Equestria B from Nightmare Moon').

Possibly take two very different Equestrias from existing fanfiction. (E.g., one of them has Nyx in it.)

Bonus: Write from the perspective of somepony working in the trade business between worlds.
Bonus: Trixie is traveling all across an unfamiliar land to... find Trixie.
Bonus: Celestia and Celestia discuss current news from both worlds over tea.
Bonus: Double date between two different ships with one identical partner each, with all the awkward conversation that comes with it. (E.g. Twi X Flash Sentry and Twi X Applejack)

There's plenty of fiction wherein the Mane6 either end up stranded in an alternate Equestria and/or meet their displaced counterparts. It usually ends with them parting ways, never to meet again.

What, if they didn't part ways?

What, if one Equestria had resources and knowledge the other lacked, and vice versa?

And what, if the portal was opened to the general public?

Title: Mutual Interest is Magic (or something... meh)
Characters: x,y ϵ {Tirek, Chrysalis, The 'Nightmare', Other unreformed MLP-villains}

During their allied siege on Equestria, two villains learn the value of friendship.

They both initially start out with plans to betray each other... later.

They end up making up excuses to themselves to put it off just one more day, just one more battle, etc.

"No, betraying him/her now would leave me weakened towards the ponies... I must wait until a better opportunity arises..."

Culminates in a scene where one saves the other from harm during a battle with the Mane6 / Celestia.

Bonus, if by the end, they both DIDN'T get reformed. Well. Not in the conventional sense, anyway.
(How would the Mane6 use the magic of friendship to fight villains that are friends with each other, anyway?)