Another thing I found in the archive.  This time it has my name on it, so now I'm SURE that I'm not accidentally ("accidentally") stealing someone else's work and mistaking it for my own.  Jesus, I barely remember doing this.

Prompt:
>Anonymous and Rainbow Dash are horsemarried. 
>Dash goes with Anon's desire for monogamy even though it feels a little strange to her. 
>One day, Dash and Scoots have a heart to heart. 
>Scoots is worried that she's going to be forever alone after some especially harsh bullying that day.
>Dash gets a bright idea(?)
>Anon is then shanghaied into letting Scootaloo into their herd. Or at least promising her a spot when she's older. 
>Anon has no idea how to feel.
>Rainbow is glad to help her surrogate sister. 
>Scoots is gif related to every other filly in town.

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"You what to to WHAT?"
>"C'mon, babe, do it for me? Please?
>She's giving you the pouty face, but you aren't having it.
"Dashie, we talked about this. You know how I feel about herds."
>"I know, honey, but Scoots needs this. You don't know how bad it is for her."
>You don't say anything, but instead give her The Look.
>Every sitcom husband knows The Look; it's the face their wives give them when they're about to do something stupid, like try to renovate the basement, or buy a new TV.
>It's the only warning they get before they end up having a slapstick adventure full of foolish decisions and long, awkward pauses for audience laughter.
>Rainbow Dash takes a step back and instinctively wraps her tail around her crotch to protect her privates.
>"A-anon? Sweetheart? Love of my life? Maybe just try it for a week or two?"
>The Look persists, and Rainbow Dash begins to sweat.
>"I kn-know you've had your eye on th-that new squad of Hyperspace Hyperwars figurines. M-maybe I could pop by the games store and pick them up for you."
>Ooooh... You're actually half-way tempted to agree, now.
>Eeehh.....
>Dash sees your temptation and barrels on.
>"I'll even do that thing in bed that we almost never do."
>BRO
>Missionary position?!
>You NEVER get to do it in missionary position!
>Ponies HATE that!
>Yeah, sure, you can put up with babysitting Scootaloo for a week.

>You are Rainbow Dash
>You're seriously throwing away all of your trump cards with this one.
>It's kind of weird to be the one who rewards their partner with sex.
>Your old herdcolt only ever let you do anal on your birthday or whenever he wanted something, but Anon LOVES it.
>It was so cute when he thought he had to ASK you if you wanted to get bucked in the plothole.
>But missionary position is almost too kinky, even for you.
>Looking into each other's eyes.... breathing each other's breath...
>Oh, Anon can be such a kinky whore sometimes...
>It's a little embarrassing to be shacked up with a colt who's such a slut, but you love him all the same.
>Anon is humming and hawing, and you just KNOW he's stretching it out just to torment you.
>Bucking colts, mare.
>"Done deal."
>Yes!
>Yes, yes, yes!
>Who's the best sister in Equestria?
>This mare right here!
"Thanks, babe! You won't regret this, I promise!"
>You fly up and give him a quick peck on the cheek.
>You'll deal with your aching wallet later; you've got a flightless pegasus you've left on a high-up cloud to break the good news to!

>You are Scootaloo.
>It's been a few hours since your idol flew away and left you on this one cloud.
>But she'll be back!
>She'll be back.
>She said that she was going to have a surprise for you, and you love surprises!
[spoiler]>You really hope that surprise isn't parental abandonment.[/spoiler]
[spoiler]>Because that isn't a surprise to you any more.[/spoiler]
>In fact, you think you might see her right now on the horizon.
>Speak of the she-devil and she will appear.
>"Good news, Scootaloo! You know that big green ape you have a crush on?"
>SHE KNOWS?!
>You thought you were so subtle!
>How did she ever spot your face pressed up against their bedroom window?!
>No, just play it cool, Scoots.
>Big mares don't panic like little colts.
>And Rainbow Dash says that you're a big mare now.
[spoiler]>For you.[/spoiler]
[spoiler]>That's what Rainbow Dash says sometimes. You don't really know what she means.[/spoiler]
>"Weeellll.... I talked to the big guy, and I rreaaallly cranked up the charm with him."
>Rainbow Dash strikes a heroic pose, and you're pretty sure you have the mare's version of a half-chub.
>"I puffed up my tuft, stood my ground, and he got the biggest bulge in his human pants. Then he agreed to try out herding with you."
>Oh.
>Your.
>Luna.
>Buck not looking like a little colt!
>This is amazing!
>Oh wow!
>You do an excited little dance while Rainbow Dash laughs with you.
[spoiler]>Not AT you, you think.[/spoiler]
>Rainbow Dash grabs you and plunks you square on her back and instructs you to grab hole of her mane.
>"That's right, kiddo! Yer on trial period. Now, let's go meet that big bag of dicks!"
>Bag of...?
>You're pretty sure that doesn't mean what she thinks that means.

>Be Anon
>Be reading a book in your favourite armchair.
>Your "I'm-about-to-fuck-a-child" senses are tingling.
>You don't really want to talk about how you recognize that as a distinct sense, so let's just move on.
>While you're busy trying to forget your dark past, you barely notice the kitchen window smashing open.
>Rainbow: "Oh, Anaawwwn! Guess who I'VE got!?"
>Boy howdy, it had sure better not be a child for you to fuck.
>Rainbow: "It's Scoots!"
>GOD DAMMIT
>Your perfect waifu comes prancing into the room with an excited orange filly on her back.
>Said filly has the biggest smile on her face and two big wing-erections on her back.
[spoiler]>Are you about to take off flying, or are you just happy to see me?[/spoiler]
>Scootaloo: "Hi, Anon! Rainbow Dash told me that you agreed to let me try out being in your herd!"
>This is not the baby-sitting position you agreed to.
>No wonder Missionary-Position was promised.
"Er, yup! Yup, yup, yup."
>You give the tiny baby filly a thumbs-up. This gesture has only just been recently understood by the pony community at large.
"Welcome to the team, Scootaloo!"
>Scootaloo jumps off of Dashie's back and hops up onto your lap.
>Aww.
>She trots around in a circle a few times and then lays down.
>How can your filly-friend be this cute?
>She places her hoof on your junk and gives it a squeeze with the frog of her hoof.
>This is less than cute.
>Rainbow: "See? Look at that! Her first instinct is to try and please her stallion. She's perfect!"

>You gently remove Scootaloo's hoof from your penis and start running your fingers through her mane.
>This always gets Dashie to calm down, so maybe it'll work on Scootaloo.
>Maybe you'll get lucky and it'll turn out to be a pegasus thing.
"She's also a filly."
>Rainbow Dash just rolls her eyes and hops up on the armrest.
>Rainbow: "Babe, we've been over this. There are something like, what, ten stallions in Ponyville, excluding yourself?"
>You nod while you pet Scootaloo like a cat.
>Scoots has no complaints.
>Rainbow: "This town has a population of a few hundred mares. Unless we want to admit to being dykes..."
>Rainbow Dash gets a little sweaty and makes sure not to look at Scootaloo.
>Rainbow: "...which I am NOT..."
>Uh-huh.
>Sure thing, Rainbow "let me gather this girl-pony to watch you fuck" Dash.
>Rainbow: "...then we can't afford to be wait until we're older to get a colt. Besides."
>She gets this look on her face that's somewhere between affection and condescending and pats your cheek.
>Rainbow: "We know you colts need a big, strong mare to look after them."
>Yeah, yeah.
"You just remember who sticks things up your butt, Dash."
>Rainbow looks worried for a moment, but she focuses on Scootaloo instead.
>Rainbow: "D'aww. Looks like he's taken a liking to you, Scoots."
>What?
>You look down and turns out you've been rubbing Scootaloo's belly.
>Scootaloo: "Awwwhawhawhaw yeahh... Keep those hoof-spiders going, Anon..."
>One of her back legs kicks and you pick things up a notch.
>Scootaloo: "D-don't stop!"
>You look up, and Rainbow Dash seems to be getting a little hot under the metaphorical collar.
>Rainbow: "Belly rubs? On our favourite chair?"
>Her penis-wings become diamonds.
>Rainbow: "Th-that's so dirty."