One More Time (Chapter 1)

Dipper Pines sat on his bed, writing down some notes, as his twin Mabel laid on her stomach on the floor, reading a magazine
"Hey Dip" Mabel said, looking up from the magazine she was reading "Wanna go monster hunting?" the boy looked up from his notebook
"Sure, after lunch?" he asked, his twin nodded giving him a brace filled smile, as Dipper hadn't gone monster hunting since the Weirdmaggedon event with Bill Cipher, mostly spending his time with their great uncle Ford down at the lab underneath the house. She returned to her magazine until they heard a loud crash come from the Gift Shop
"What was that!?" Mabel yelled looking at her twin
"I don't know, come on" Dipper said, running down the stairs, Mabel right behind him
"What the heck Pointdexter?!" a gruff voice yelled as the twins reached the door to the gift shop "Do you know how hard this thing was to find?" Mabel gulped and opened the door, showing their grand uncles arguing, Stan pointing at a large object covered in a tarp leaning on the register counter, Wendy reading a magazine trying to ignore the arguing twins
"Yes I know, because I hid it!" Ford yelled "Stan that thing is dangerous!" Stan rolled his eyes
"Pointdexter, a few days ago, you thought the coffee maker was dangerous" he pointed out "Your being paranoid"
"Okay, first I'll admit I was wrong about the coffee machine" Ford said "But second, I've seen and studied this thing! If were not careful, it could be very dangerous. Almost a dangerous as Bi-"
"Grunkle Ford!" the twins hissed, Ford bit his tongue before he finished the sentence
"Almost as dangerous as what?" Stan asked, glarng at his brother daring him to answer "Like I thought" he said, a smug grin on his face as he turned around to grab his new exhibit
"That was close" Mabel said, walking over to her great uncle
"Grunkle Ford, you know cant mention Bill" Dipper whispered
"I know, it slipped my mind for a second" Ford said, rubbing his hand through his hair
"Now, if your done being paranoid Ford" Stan said, dropping the object in front of them "Look at this baby!" he yanked the tarp off to reveal
"...Is that a mirror?" Mabel asked, unimpressed
"Yes, but not a normal one" Stan said as he hing it on the wall opposite to the entrance allowing the twins to have a better look at it. It was a large circular mirror, shiny as if was just cleaned, but the frame was the interesting thing it was blue on the left with rubies and red on the right with diamonds, split evenly down the middle
"Why didn't you take one of the gems off?" Dipper asked
"Tried" Stan said, throwing the tarp to Wendy "Won't come off. But this trick is what going to make us some cash"
"Trick?" Mabel asked as Stan walked over to the mirror with a cup of water "What are you doing?" Stan simply smiled as he threw the water at the mirror, splashing on the glass surface but not a single drop fell, instead spreading over the whole thing
"Alright, take a look" the conman said with a flourish of his arm, Dipper shrugged stared at his reflection on the mirror
"There nothing-" Dipper started to say as the image started rippling, when it stopped, a version of him dressed very differently. The boy in the mirror wasn't wearing his hat, he had a blue T-shirt with a yellow star on it and a band-aid on his chin "Okay, that really weird" he squinted, seeing that his doppelganger had braces "Grunkle Stan, where did you get this thing?"
"Remember Pointdexter's hidden bunker?" the twins nodded "Well I found this right next to the entrance. Now you two get to work, the buses will be here soon" as soon as Stan walked off, the twins ran to Ford
"Is that thing really dangerous?" Mable asked him
"Potentially" the Author explained "The mirror is actually a Dimensional Rift."
"WHAT!" the twins shouted, eyeing the mirror before Ford chuckled
"Don't worry, it's linked to a specific world. That's why you see a different version of yourself when you look into it" Ford explained as the sound of a bus pulling up "Well, we better get to work"

Dipper sighted, sweeping the floor next to the counter as Wendy flipped through a magazine, Mabel ran around offering people things
"Hey dude" Wendy asked him "Does that weird mirror work?"
"Yeah it does" he said "When I looked into it, I saw another version of me"
"Cool" the redhead said, putting down her issue of 'Avoid Eye Contact Monthly' "So, what did you look like?" before Dipper could answer, the door to Shack flew open, an enormous gust of wind knocking almost everything off the shelves
"The heck?!" Wendy yelled, the lights suddenly dimming "What's going on?" Dipper didn't answer, instead he pointed towards the open door, the redhead looked and gasped at the creature he saw. It was around 9 feet tall, lanky and extremely skinny almost like it had never eaten in its life, it was pitch black with no features or mouth. The only thing that drew their attention was the monster's glowing purple eyes as it scanned the room, Dipper didn't notice his sister run past him towards the employees only, his eyes were glued to monster in front of him.
"What are you?" Dipper whispered, the monster suddenly froze and turned its head towards him. The twelve year old gulped, the monster hadn't realized he was there "Wha-what do you want?" the monster simply stared at him, dark grey smoke was starting to emminate from it's arms and snaking towards him
"....Mirror..." a monster said, without any movement of its mouth. Before Dipper could respond, the smoke had made its way to him and he breathed it in
"Ach!" Dipper grunted choking "What do you-" he stopped his sentence as the Gift Shop blurred out, he started hearing laughter fill the room "Where is that coming from?" he thought, before he looked and froze. He was wearing the lamb costume he used to wear when he was 4
"Hahaha!" the laughter around grew louder and louder, up to the point he covered his ears witch didn't help, he closed his eyes in desperation
"Come on dance, Lamby! Dance!" a familiar voice yelled among the laughter, he opened his eyes and gasped, the gift shop was gone, he was standing in black void surrounded by people, including Mabel, Stan, Soos and Wendy, most pointing and laughing at him
"Dance!" they all yelled together "Dance! Dance!"
"SHUT UP!" he yelled, hyperventilating slightly, tears forming in his eyes "I'M NOT GONNA DO THAT STUPID DANCE!" his screams fell on deaf hears, the crowd kept yelling for him to do the Lamby Lamby dance, he thought he heard someone call his name but it drowned out by the laughter and instance of dancing