A/N Hey guys! Sorry I'm late with The Sonic/Undertale crossover. I'll get going on that soon but I am starting another series and this is it! It has skele-TONS of references. There will be some Underverse things in here like that and a bit of Camila in it so enjoy! Also, the codes are important though they might not seem like it. Hint: The bold and underlined words are not from the same person. Also, A-1 and Z-26! Have fun!

Dipper exited the bus and looked at the old, decrepit house in front of him. The house was clearly not up to code and the building looked like it would fall apart any second. On top of the building was a sign that read "Mystery Shack." The "S" had fallen off of the sign and on to the roof.

"I guess this is it." He shrugged as if to shrug off the feeling that they were at the wrong place. This is it. The place he and his sister, Mabel, would be staying for the Summer.

Looking back, he looked at the bus for Mabel. He didn't have to look far into the bus for her.

"A little glitter to make your day SPARKLY!" She said to the bus driver, throwing glitter at the grumpy bus driver who clearly put up a fake smile to stop her from throwing glitter at him.

"I didn't get paid enough when I worked with Mettaton, I don't get paid enough to deal with this. I don't know why I thought any different." The bus driver grumbled under his breath as Mabel stepped down the stairs of the bus with a wide smile.

The bus drove away (a little faster than it should've) as Mabel joined her brother, her smile so infectious she made Dipper smile a bit. She turned from her brother to the building. Her smile got only larger.

"I'm so excited, Dipper! If the building has a history, think of what our Grunkle will be like!" Mabel wrapped her arm around Dipper as they moved towards the steps to the porch.

"I doubt the 'Mystery Shack' has any historical relevance if the government allowed our Great Uncle to live and make a store out of it." Dipper replied, still hesitant about meeting their Great Uncle.

"Stop with your nerd talk! I didn't need to learn how the government works." Mabel retorted, causing Dipper to roll his eyes in disbelief.

"Also, Grunkle?"

"Yup! It's a mix of 'great' and 'uncle'. We can't call him, 'Great Uncle' everytime we want to ask him something and let's face it. We'll be asking for a lot of things while we're here!" Mabel giggled as she walked up the steps to the front door.

"Get ready to meet our Grunkle!" Mabel yelled to Dipper as she knocked on the door. Dipper joined her. They waited.

Dipper wondered what their Grunkle would look like. Was he smart? Would he engage Dipper in philosophical discussions? Would he be funny? Would he amuse Mabel? ...What's his name? Dipper panicked. How could he forget his name?! His Dad repeated it multiple times! What eventually pulled Dipper back from his thoughts was the door opening.

The person who opened the door looked at the twins with a smile. He was as tall as the Twins. His hair was shock white and his eyes were bluish-grey. He wore a white shirt that was partially covered by a blue jacket and black exercise shorts that didn't cover up the fact he was wearing slippers. He was about to speak when Mabel beat him to it.

"GRUNKLE SANS!" She shouted before jumping onto the man. He let out a startled grunt before falling over.

"Woah! Are you okay?" Dipper said, worried for his Grunkle.

"'m okay. i didn't know she could a-DOOR me already!" The man winked and Mabel, still on top of him, giggled and Dipper smiled.

"So... are you Grunkle Sans?" Dipper asked.

Pushing Mabel off, he stood up and brushed his jacket.

"the one and only. you must be my great nephew, dipper and this troublemaker," he pointed to Mabel who was laughing on the floor. "must be your sister, mabel." Sans's smile widened into a big toothy grin. "where are my manners? welcome to the mystery shack, the one stop place for jokes and pranks."

The Twins went into the building. Unlike the outside, it didn't look wrecked at all. There were shelves full of joke books, whoopee cushions, and items that prank the people who pick them up. A sign was hung up, written in Comic Sans that said, "the name, 'mystery shack' is a prank to catch tourists. if you're a tourist, enjoy these pranks and jokes that are at on sale all the time."

A red-headed teenage girl was at the cash register, lazily watching a young kid in a poncho reenact an event she witnessed in gripping detail. A man with a green question mark shirt was fixing a pipe. Grunkle Sans closed the door behind the twins. Mabel wowed at every item in the aisles, sometimes trying them out on herself. Dipper, in the mean time, looked at his Grunkle, who was watching Mabel playfully try to flirt with an attractive wax statue ("so lifelike").

Dipper could see that his Grunkle's smile was genuine but his eyes told another tale. His grey eyes seemed to say that he was tired or that he had experienced untold pain in his past and he was just happy to finally have a little light for the summer. As Sans turned to look at Dipper in confusion, he sheepishly went over to where the sleepy teen and energetic kid were talking.

"And then Undyne was all like 'WHOOSH!' and 'KAPOOSH!' and the gnomes were all like, 'Oh no! Spears!' and then they ran away and Undyne yelled, 'YEAH! GO RUN, YOU LITTLE FREAKS! IF YOU TRY MAKING SOMEONE ELSE YOUR QUEEN, I WILL MAKE YOU DECORATIONS ON MY LAWN! NGGGGHHHHH!' and then she surplexed a boulder and she was so cool!" The kid that looked around Dipper and Mabel's age took a breath before composing herself. "And that's why I can't be queen of the gnomes."

The kid looked winded and she pulled off the hood of her monster-themed poncho to reveal orange hair as she wiped her brow. Her hands and arms were obscured by the poncho which, for some odd reason, didn't have any place for the arms to go. The poncho also included a tail. The red-headed teen let out a friendly laugh.

"You must really like the Sheriff, MK." She replied.

"Oh yeah! Undyne's so cool! She's my hero! When I grow up, I want to be just like her." The girl all of a sudden noticed Dipper standing and watching the conversation. Before he could back out and look like he wasn't eavesdropping, he was caught.

"Yo, Dude!" The girl said, as she ran up to meet him. "I haven't seen you before? Are you new? Did you move here?"

"Naw, MK. He's Sans's great-nephew. You know, the one Sans has been mentioning for a week?" The teenager said before Dipper could respond.

"Yeah." Replied Dipper, rubbing his arm. "My name is Dipper Pines."

"No way! That's an awesome name! Name's Mon- er... Mary Kathrine but you can call me MK for short!" The kid in the poncho responded.

"Name's Wendy." The teen raised her hand in acknowledgement.

"No way!" A voice shouted, scaring Dipper before he realized it was Mabel. She was holding onto MK's poncho by the tail, staring at it in amazement. "I love your Poncho! Where'd you get it, Mikay?"

MK smiled as she realized she got a new name or nickname to be called by.

"If I'm perfectly honest, I don't know where my parents got it from but from the looks of your sweater, you could make one on your own!" MK smiled at the sweater that was so glittery that you almost had to wear sunglasses to see it.

Mabel blushed. "Awww. Thanks!"

Sans came up to the cash register and looked at Wendy. "you can go home early, if you want, wendy." Sans said with a shrug.

"Thanks, Mr. Pines." Wendy picked up her stuff including a magazine and headed to the door.

"See ya guys tomorrow." She said. "And welcome to Gravity Falls." Then she left through the door.

Sans turned to the man with a question mark shirt. "you can go home early too, soos."

"And miss out on this action? Not a chance, Mr. Pines!" Soos turned back to the pipe. "Let's see... I always forget. Is it... lefty tighty, righty loosey?"

Soos turned the wrench to the left, causing the pipe to come crashing down and water to come streaming down. Dipper looked worriedly at Sans. Sans was looking at what happened like as though it happens everyday.

"Don't worry, Mr. Pines. I will clean this mess up." Soos said, just as concerned about it as Sans was.

"well, I never doubt you, soos. i'll be taking dipper and mabel to their room." Sans said with a shrug. He then lazily walked to the back of the shack with his hands in his pocket.

"Grunkle Sans, where is our room?" Dipper asked politely.

"And most importantly, is it sparkly?" Mabel replied with a serious face that hid her joking nature.

"well, we're gonna go into that main house." Sans replied before they reached a door that had a sign that said, "employees only (but if you go in, it's not like i can stop you or anything)".

When Sans opened the door, Dipper and Mabel saw a colorful room. The wall was a shade of dark red and the carpet was blue and purple in a wavy striped pattern. To their right was a table with four chairs surrounding it with a center piece of a rock covered in sprinkles. To their left was a green couch that was right in front of a tv and to the left of that couch was a coffee table that had a book on it. In front of them was the kitchen that had a fridge, an oven, a really high sink, a normal sized sink and a trash can.

"sorry if it's a mess." Sans said in his lazy voice as he looked to a sock that was covered in Post-it notes (not a product placement). "i don't get many visitors anymore."

"What are you saying?!" Mabel said, excitement filling her face. "It's PERFECT! I love it! Where am I sleeping?"

"well, technically this is the living room." Sans said as he sauntered to some stairs in the upper left corner. "your room is upstairs."

Before Sans could reach the top, Mabel rushed past him, almost making him lose his balance.

"Grunkle Sans?" Dipper asked as he walked right beside Sans. "I have a question."

"shoot, kid."

"Why do you have four chairs when there are only three of us?" Dipper watched as his Grunkle's grin fell a little flat. His eyes were pained. Before Dipper could press forward the question, Sans shrugged it off as his smile came back.

"Well, we could always need a CHAIR-man." He said with a smirk. Clearly, he was avoiding the question.

As they reached the second floor, three doors were there to greet them. Sans went past the first door, not even acknowledging its existence. Mabel ran ahead to the next door but Dipper stopped in front of the first door.

The door had a stop sign on it and labels. Dipper mused at the labels as to their meaning, for one said, "NO GIRLS ALLOWED!" while the second one said, "NO BOYS ALLOWED!" and then the last one said, "PAPYRUS ALLOWED." Dipper could already see mysteries unfold. Who is Papyrus? Why was Sans in pain when he was reminded of the fourth chair that was seemingly untouched? Why did he wish to forget there was a door here?

Dipper sighed as he realized that he might never know the answers if he asked his grunkle. He was going to have to piece them together. Then, Dipper heard his sister go into the next door with Sans and so he decided to join them.

The second door led to a white room with light brown carpet. A wardrobe was to the left of the door and so was a lamp. Mabel was jumping on a pink bed that was on the right. The pink bed had a shooting star on the covers. To the left was another bed that was blue and had a tree on the covers. Sans watched and smiled as Mabel continued to bounce.

"Look, Dipper! Sans bought us beds! Now I can party all night!" Said Mabel, giggling.

"heh. if i were a good guardian, i would say that you are not allowed to party all night but since i'm not, i can only warn ya." Sans said, winking before taking out a red bottle and drinking it.

"Yay for Grunkle Sans not being a good role model!" She yelled out.

Dipper let out a smirk but then turned his head to Sans who, in response to the comment, had begun to cough out the liquid that he had swallowed the wrong way. Luckily, he managed to recover with a smirk on his face and Dipper was glad that he didn't have to use Heimlich Maneuver on anyone yet.

"Thank you, Sans, for the beds. You didn't have to... uh... you know... buy them. We have sleeping bags." Dipper said, looking down at his feet as he rubbed his arm.

"naw, kid. these beds were on sale at the local mattress shop. anyways, i can't let my family sleep on the floor." Sans winked at Dipper.

Mabel laughed. Then, while she jumped in the air, moved herself to land on the floor to make a stunning landing. Unfortunately, she didn't quite stick the landing, causing her to fall on her belly. She looked up, laughing. When she looked to her Grunkle, she could've sworn that she saw his right eye glow blue a little bit. Then, he shook off the shock.

"ehhh... you goofballs. why don't you guys go explore the town? there are tons of people i think you would find friendly." Sans said as he stood up. "i'll be hanging out around here to continue the business with soos." He went through the door before turning towards the twins again. "oh. by the way, the door to the right of you room is my room. you can't enter because you need a key to open it but if you want to come in, you can knock and say a knock-knock joke, if you want." Sans shrugged before leaving.

Dipper waited until he heard his grunkle leave the hall and back into the shop before asking the question buzzing through his mind.

"Mabel, what do you think of Grunkle Sans?" He asked, unsure of his own answer.

"I think he is great! He has a sense of humor and he has allowed us to explore the town!" Mabel said, getting up off the ground and getting ready to bolt through the door to the town.

Dipper got in the way of Mabel. "But he has a lot of secrets, Mabel. Like the door with the signs and the extra chair and his room! How can we be sure that he isn't some mass murderer or something?"

Mabel's smile fell a little bit. "Dipper, he clearly cares about us already. If he were going to kill us, he could have done it already. Sure. I see the mysteries too but since I believe he is a good guy, I think those mysteries are things he'll tell us eventually." Mabel smiled a little and it instantly made Dipper forget his doubts and smile too.

"Maybe you're right. I'm probably just paranoid from reading all those mystery novels." Dipper said. "But I can get to the town before you!" At that, Dipper ran through the door and laughed.

"Hey! No fair!" Mabel shouted before running after her brother.

The twins said hi to Sans as they left the Mystery Shack and Sans, who had his head on the table and was about to take a nap, opened one eye to say goodbye. As he closed his eyes, he tried to push away the bittersweet memories that the Twins reminded him of.

Dipper was in the lead but only because he had a head start. To compensate for the disadvantage of his lack of muscles, his mind told him to run through the forest so that she might get farther behind. He found the plan had worked to his advantage as Mabel fell farther behind. When he couldn't even hear her panting and giggling, he stopped for a quick breath.

Dipper wiped his brow before putting his hand on a tree to help support him. Suddenly, his hand sinked a little bit into the tree. Dipper looked to his hand to see that he had triggered something. Pulling his hand off, he realized it was a button of some kind that was exactly hand shaped. Then, he heard mechanisms trigger as the tree opened up to reveal a metal compartment in the tree.

"What on earth..." Dipper said to himself as he looked inside. Inside, through the dust and cobwebs, was a book.

Curious, Dipper pulled out the book and blew the dust off of the cover and marveled at what he had just found. The book's leather cover held the image of a golden hand. Dipper wouldn't have found this interesting if it weren't for the fact that the hand had a hole right in the middle of it. In the middle of the hole was the number, "3".

Even more intrigued than before, he opened to the first page of the book and read aloud.

"In my research of this area, I have found that there are items, places, and creatures that are supernatural in origin. Gravity Falls is not what the locals say it is, and nobody is to be trusted. That is why I will leave this book, that when paired with malevolent intention can be dangerous and lethal, in hiding until someone finds it or this Pine Tree falls. Thus, to the owner of this journal, TRUST NO ONE!"

Dipper gasped. This was it. This could be the adventure of the lifetime if this journal were true... or the writer could just be a crazy person. Either way, Dipper needed to know. He skimmed through the pages of supernatural creatures and places, looking for a name, an identifier, or anything that could identify the Author but to no avail. He had found a mystery and this time, he would not let it go unresolved.

Keeping the Author's warning in mind, he hid the book, sighed as he realized he lost the race with Mabel, and started running to the town.

23-8-1-20 8-1-19 2-12-21-5 5-25-5-19, 19-13-9-12-5-19 1-12-12 20-8-5 20-9-13-5, 1-14-4 9-19 9-20 5-13-15-20-9-15-14-1-12 16-1-9-14 5-22-5-18-25-4-1-25?

1 3-15-13-5-4-9-1-14