“Absolutely not!” Flash replied emphatically to his teenage younger brother.
“Come on, Bro, please,” First Base begged. “Your marriage only happens once. I might not get another chance.”
“Which is exactly why you SHOULDN’T even be planning on pulling any pranks. Remember what happened when you pranked Sweetie Belle during the last rehearsal we had for the reception?”
Four days earlier…
“Listen here, you little punk,” Sweetie practically screamed as her voice went up a few octaves in rage. She was holding onto Base by his shirtfront, and her face was so close to his that he could see the blood-gorged vessels in the whites of her eyes. “If you Rein on me even one more time, I will bludgeon you with whatever I have in my hand for HOWEVER LONG IT TAKES FOR YOU TO DIE!”
Any fury Sweetie had left over after her outburst came out in several steaming huffs and puffs. First Base grinned nervously as his eyes remained locked on Sweetie’s bloodshot ones.
“Why in the world does Button Mash find you so attractive?” he blurted out.
“What?” Sweetie replied, Base’s question shocking her out of her wrath.
“What?!” Button shouted from behind the soundboard. His eyes bulged out and his jaw dropped in shock before his whole face contorted into an expression of utter betrayal.
Realizing what he had just uttered, First Base cringed so hard that he literally bit his tongue.
“Uh, did I say that out loud?” he squeaked out, giggling uncomfortably.
Meanwhile, Flash and his fiancée Twilight were watching the whole fiasco from a short distance away. Twilight raised an eyebrow in confusion while Flash cringed and put a hand over his face.
“He’s not planning on doing that during the actual reception, is he?” Twilight asked Flash.
“I sure hope not,” Flash muttered with his hand still covering his eyes.
Back in the present…
“Yeah,” Base conceded sheepishly. “Button is still a little mad at me for accidently letting his secret out, and Sweetie is still a lot mad at me for Reining on her again. Serves me right for pulling the same prank on the same person twice, but the prank I have in mind is different this time, honest.”
“Bro, I DO NOT want my wedding day to be the day you end up bludgeoned to death by one of Twilight’s friends’ younger sisters,” Flash exclaimed. “Why don’t you just tell me what you’re planning so that I can tell you if it’s a good idea or not?”
“Because I’ll lose the element of surprise and it won’t be a prank anymore, duh,” he replied, giving his older brother a flat stare.
“Lose the element of surprise on who?”
“I can’t tell you that either.”
Flash stared back at Base and pinched the bridge of his nose groaning, “Is there anything that you CAN tell me about what you’re planning on doing?”
“Just that it doesn’t involve Rein Astley songs or Sweetie Belle.”
Flash stared at Base some more as he continued to contemplate an appropriate response. Now, Flash knew that his brother never intends anything mean-spirited with his pranks and jokes. In fact, entertaining people and making them laugh was just how Base showed affection, and Base had only started embracing that side of himself within the last two years thanks to Flash’s encouragement. However, as the incident with Sweetie Belle indicated, Base had yet to master the art of knowing his audience. Besides, that day is going to be as much Twilight’s wedding day as it is going to be his, and the last thing Flash wanted was for his brother to unintentionally upset his soon-to-be wife.
“I’m not saying that I agree to it,” Flash began, finally speaking, “but if I am going to agree to it, we need to set a few ground rules. One, no one can end up hurt, injured, or dead.”
“Of course not,” Base scoffed incredulously. “What kind of a jerk do you think I am? I’m not going to injure or kill someone on your wedding day. Or on any other occasion, special or otherwise.”
“Two, you can’t insult, offend, or anger anyone, not Sweetie Belle, not any of the other guests, and especially not Twilight and her family.”
“No problem,” Base affirmed confidently before backpedaling a bit. “No, wait. There might be one problem.”
“What?”
“How am I supposed to guarantee no one will get mad? I mean, what I have in mind is more meant to be funny than offensive, but I can’t control how other people are going to react to it.”
Flash sighed, pinching the bridge of his nose again, “What are the odds that your prank, whatever it is, is going to get the same reaction that you got out of Sweetie Belle?”
“If I do it right and if everyone has a good sense of humor, none.”
Neither of the brothers said anything for a while. Flash was still trying to find a reasonable answer to his brother’s request, and Base was still waiting for Flash to give it. Finally, Flash threw his arms in the air and looked his brother in the eye.
“Okay, alright, I’m going to make the really questionable decision of trusting you,” Flash answered sternly. “Don’t make me regret it.”
“You won’t,” Base assured him, extending his right pinkie finger towards his older brother. “Pinkie swear.”
Two days later…
“Daaaaaaaance/I hope you dance,” Sweetie Belle sang from the stage set up in an adequately sized banquet hall. “I hope you dance.”
Sweetie Belle’s older sister Rarity and Twilight’s other friends, formerly known as the Rainbooms, accompanied the teen girl on their instruments while Applejack and Apple Bloom’s older brother Big Mac provided the backup vocals. Out on the dance floor just in front of the stage, Twilight Sparkle glided across the floor in a gorgeous white gown with her father while her newlywed husband and his aunt waited their turn for the “mother”-son dance. Off to the side of the stage, First Base giddily waited his turn to perform the song for the next dance.
“Tell me, who wants to look back on their years/And wonder where those years have gone?” Big Mac closed the song as the Rainbooms played the last note on their instruments, and Twilight and her father finished their dance to the applause of all the guests.
As Twilight and her father left the dance floor, Flash and Aunt Flare took their place on it. Meanwhile, on the stage, Sweetie Belle, Big Mac, and the Rainbooms got off as First Base and Flash’s old bandmates Brawly Beats and Ringo got on. Sunset Shimmer, however, stayed on stage with her guitar since the former Flash Drive’s regular guitarist was currently out on the dance floor. Base took his place at the microphone while the rest of the band began to play.
“Hope when you take that jump, you don't fear the fall,” First Base began to sing. “Hope when the water rises, you built a wall/Hope when the crowd screams out, it's screaming your name/Hope if everybody runs, you choose to stay”
The rest of the song and dance went as expected until Base got close to the chorus.
“And I hope that you don't suffer but take the pain” Nobody noticed it, but as Base began to close the first verse, the corners of his mouth twitched upwards mischievously, and his eyes gleamed in anticipation. “Hope when the moment comes, you'll say:”
“IIIIIIIIIIIIIIIIIIIIIIII, I did it all!” First Base was standing behind the microphone, and his lips were moving, but his voice wasn’t coming out of the speakers. Instead, Donald Duck was heard belting out the first two lines of the chorus. “IIIIIIIIIIIIIIIIIIIIIIII, I did it all!”
Flash stopped dancing and doubled over laughing. Shortly after, Aunt Flare was laughing as well. Base sang the next two lines in Scrooge McDuck’s voice, which made Shining Armor and Cadance laugh, which made their one-year-old daughter Flurry Heart laugh. Twilight, her parents, and Grandma Birdie started laughing as well, and soon, almost everybody in the room was laughing. Even Base’s accompaniment was struggling to control their laughter well enough to play their instruments.
“With every broken bone I swear I lived,” Base closed the chorus, switching back to his Donald Duck voice. He signaled for his accompaniment to stop playing, and once the laughter had died down, he spoke into the microphone in his normal speaking voice, “So, that was a little wedding gift from me to the best older brother in the world. I just thought he and Twilight would appreciate sharing good laugh with all the people who love them to start their new life together.”
That last statement elicited another round of laughter from everyone in attendance and bright smiles from the happy couple.
“Now, I’d say more, but the speeches aren’t supposed to start until later tonight, and I know how my new sister-in-law is with schedules, so I think I’m just going to finish singing this song so that my brother can finish dancing with our aunt.”
Even though Twilight was giving First Base a rather annoyed glare, she couldn’t help but smile and laugh along with everyone else. Base signaled for Sunset, Brawly, and Ringo to start playing again, and the rest of the night continued with everyone in lighter spirits. In the end, Base had given Flash a gift only a brother could appreciate, and neither of them had anything to regret that night.
Author's Note
Okay, so, prompt of the day is "Twist," and the first place my mind went to, regarding the prompt, was pranks, specifically wedding pranks. 
Yeah, I know that for a FlashLight Week fic, there was barely any FlashLight in this, but this was what I came up with. Besides, in my series, Flash's relationship with his family, especially his younger brother, make up a huge chunk of who he is, and I just had to both highlight Flash and Base's relationship and let First Base in on the fun. 
Furthermore, at the end of the story, Flash and Twilight are happy, married, and laughing. Surely, that counts for something. Right? 
By the way, in case it wasn't obvious, part of this story takes place before Flash and Twilight's wedding, and the other part takes place during the reception, so chronologically, this takes place before my first two FlashLight Week submissions.