This side story is taking place at the same time Arc 2 of Big Macintosh: the Stallion of many mares. While this is the anthro world, Discord remains the same since he already walks on two feet, sort of.
In Fluttershy's cottage, Fluttershy was helping one of her animal patients. As she was bandaging the patient up, she heard a knock on the door. At first she thought it was one of her friends, but it was actually Fleetfoot and Tealove. Fleetfoot told Fluttershy that they needed to talk about something important right now at "the house". When Fluttershy heard that word, she left food for Angel and left with Fleetfoot and Tealove. The three mares went to a secluded place and used the keys that they can enter the secret house to meet with Big Mac anytime they like to screw around with him. They went into one of the various rooms so they could talk.
"What seems to be the problem" said Fluttershy.
"More like problems. Big Mac is in Manehattan doing pornography to payback a favor that Princess Luna owed Rarity for making us those costumes that we wore to please Big Mac. To make matters worse, Cheerilee and Marble Pie sneaked off to Manehattan to try and get some extra time with Big Mac on their own." said Tealove with a panicked look on her face
"We have to do something to up our game. Big Mac is going to be surrounded by different mares that will cause our harem to start increasing. If that happens, Big Mac will look to his new mares more than us. We need to figure out what we're going to do in order for Big Mac to pay attention to only us." said Fleetfoot.
"We could just trap him with us; you know, have his babies." said Tealove
"No Tealove; we can't do that to him. Besides, Princess Luna put a spell on Big Mac preventing his seed from ever entering us and giving birth to foals so prematurely." said Fluttershy
"What if we found someway to improve our methods? We just have to find ways to spice up our game too; no matter how crazy it is." said Fleetfoot
"There might be someone who can help us, but you two have to keep a very open mind." said Fluttershy with a serious look on her face.
In Discord's house, he was reading some magazines; these magazines are pornographic and he used his magic to make all the mares in it look like Fluttershy and all the stallions look like him. Since he has very good standing with Fluttershy, he has never tired to make any sexual moves onto her in fear of losing his only close friend. However, he does use his magic to make dolls that look like Fluttershy and he has sex with them in his spare time. He was about to grab one of them until he could hear Fluttershy knocking on his door; he made sure to hide all his magazines and dolls where she couldn't find them and answered the door.
"Oh Fluttershy, I wasn't expecting you here. And I see you brought friends." said Discord
"Discord, you can open a dimension to almost anywhere right?" said Fluttershy
"Yes!" said Discord.
"We need you to open a dimension to a place where we can learn so many sex tricks that we'll be Big Mac's center of attention." said Tealove getting in front of Fluttershy and into Discord's face.
"This about that game the princess play. I guess it's that time of the year for that." said Discord
"How do you know about it?" said Fleetfoot.
"Even while I was stone, Celestia and other alicorn princess in the past usually brought the stallions they were playing with during their game to the gardens sometimes; I remember seeing and hearing them. Who's team are you all on anyway?" said Discord hiding his irritated face from behind them
"Princess Luna's team; Big Mac is the stallion. We have to come up with a way to be his center of attention by learning new tricks that are so good that he won't be able to take his eyes off us; this is especially important since more mares are going to be joining in the game." said Tealove
"What we were hoping is if you know somepony that could help us or take us somewhere that will help, if it's not too much trouble." said Fluttershy.
"Well there is somepony that I recently met that can help you all. Her name is Lady SD. She's lives in dimension XXX-DTS. I can take you all there, but that's all I can do for you. I have something else that I need to do." said Discord
"Like what?" Fleetfoot asked him.
"It's nothing you need to worry about." said Discord hiding something while they aren't looking
"So is that the portal that will take us to dimension XXX-DTS?" Tealove asked him
"Yes! Here, just ring this bell whenever you all want to come back home." said Discord giving them a golden bell.
"Thank you Discord; you're a true friend." said Fluttershy hugging him right before going into the portal to dimension XXX-DTS with Tealove and Fleetfoot.
"That must have been hard for you; I saw your other head with a very angry look on your face." said Celestia appearing right in front of him due to an invisibility spell.
"Don't toy with me Celestia. It's bad enough that Princess Luna picked Fluttershy for her team, it's worse that she's falling for Big Mac. How long does your game last this year Celestia?" said Discord throwing darts at a picture of Big Mac
"It will be a while before it ends Discord. Besides, I thought you would use this opportunity to spy on Fluttershy's lesson from Lady SD." said Celestia
"I have some hidden cameras there, but it's still not the real thing as being a part of it or doing it myself. The only reason I'm agreeing to help you and Twilight with your scheme is to make sure that one of your mares wins so I don't lose Fluttershy to Big Mac. However, you also told me that you would give me the secret dimension that only has an entire population of Fluttershy is there and nopony else." said Discord with a pouty/jealous look on his face and smashing stone dolls shaped like Big Mac
"Patience Discord! You'll get your reward soon, just be sure to have that book ready for Twilight and make sure Fluttershy and her friends are ready for pick up later." said Celestia with an evil smirk on her face.