This is Part of the Future of Gravity AU where the twins are grown up and living in the Mystery Shack. It's based on SuperGroverAway's Future Pines AU and features some elements and characters from it. Written by me and Mystery Shack user Darth Vader.

Christmas is the best time of the year for most people. Especially for Mabel Pines. The 33 year old woman loves the holidays because of spreading cheer and cuddling with her family. As she was decorating the tree with her brother and sister in law, she constantly sang Christmas carols. "Deck the Halls with". Mabel sang before being rudely interrupted.

"Please stop sis." Dipper asked "You've been singing for an hour and a half now.".

"There's three big ways to spread Christmas Cheer brother! Presents, Cookies, and Caroling!" Mabel replied cheerfully while squishing her cheeks.

Dipper was about to respond before his wife stopped him. "Give it up doof." said Wendy. This caused Dipper to calm down a little bit.

All of a sudden, Finn and Gladys (Mabel's twins) and Phoebe (Dipper's and Wendy's daughter) came into the living room. Phoebe and Finn didn't have to say anything for Dipper and Mabel to assess the current situation. It involved Gladys, who was tangled from head to toe in silver tinsel.

"What did you do this time," Mabel asked, sighing.

"Wrapping up myself!" Gladys replied.

Mabel then smiled and said "Santa has definitely come to town!"

She then picked up her daughter and started cuddling her. Gladys was unable to escape the hug and as a result relaxed into it. When she was released, Dipper was the one who had to extricate her from the tinsel.

"So what do you want from Santa, Phoebe?"

"Someone at school told me that there's no Santa." she replied to her father.

"Of course there is a Santa." Mabel said cheerfully. "Dipper and I have traveled with him before."

"How do I know that you're not just saying that?" said Phoebe. None of our traps have worked.".

"Phoebe has a point Mom." Finn said.

"Yeah, that does sound pretty compelling," Gladys seconded.

Dipper and Mabel gave each other a worried look. They feared the day their children stopped believing in Santa.

"We'll prove that Santa's real" Wendy interrupted.

Later that night after the kids were tucked in, the twins and Wendy were discussing what to do to get the kids to believe in Santa. Mabel was feeling a little upset.

"I'm a bad mommy and auntie" she said.

Dipper immediately wrapped his arm around his twin. "No you're not." he said.

"Dipper, they don't even believe in Santa anymore!" The grown woman slumped back into Sweatertown.

"Mabel…" he sighed. "This was bound to happen. Your kids and Phoebe weren't gonna stay young forever. You knew this just as well as I did."

"But my babies need to be happy for the holidays." Mabel replied. "What should we do?"

Wendy, who originally had left to go to the bathroom, came back holding a Santa outfit. "Mabes? I found this under the rug. Why do we have this?" she asked.

"That's a long story" "I may or may not had been a mall Santa before." Mabel replied, standing up. "But I know what we can do with it."

Dipper knew that look on Mabel's face all too well. It was just a matter of time before they came up with a long, carried out plan that could yield good results. Either way, Dipper was curious to see where it would go.

10 minutes later, Mabel was wearing the Santa outfit and had forced Dipper and Waddles into wearing Elf and Rudolph costumes, causing Wendy to giggle. "Do I have to wear this sis?" Dipper asked.

"It's for the sake of our children, so yeah you do!"

Dipper had never been more afraid of his sister than he was right now. A bright flash of light dilated Dipper's pupils and he saw that his wife had taken a picture of them. She was cackling as if she were a witch.

"Hey delete that!" Dipper said to Wendy.

"No way my little elf!" Wendy replied as she continued giggling.

"Alright here's the plan." said Mabel. "First, we're going to make the living room of the Shack look like a winter wonderland. Then, Dipper and I will jump down the chimney and Wendy, you're going to bring Waddles down before the kids can get there. They believe Santa's real, and their innocence is regained."

Dipper shook his head. "I don't think this is a good idea."

"All ideas are good ideas brother!" Mabel declared causing Dipper to sigh.

"Alright people let's get to work! Wow, this beard is scratchy." said Mabel. " BTW guys, how's my Santa voice?" she sweetly asked.

"It's..great," Wendy said awkwardly, giving her a thumbs-up. She was totally guessing, seeing as she had never heard the Santa voice before.

Dipper was sent to find fake snow.

"And that's the true meaning of Christmas kids!" Mabel said in her Santa voice after readjusting her glasses. "How was that?!" she asked Wendy?

"Um, good. I guess" answered Wendy.

Dipper later returned with boxes of fake snow looking exhausted and covered in cold icy water.

"What happened broski?" Mabel asked.

"You don't want to know" he said.

Mabel ignored the comment and took the boxes of snow. She then proceeded to dump all of it over an otherwise clean TV room. Wendy and Dipper exchanged a look. This was definitely a Mabel plan.

"We're truly spreading Christmas cheer guys!" Mabel joyfully said.

The family proceeded to decorate the entire Shack with fake snow, ornaments, mistletoe, and candy for the next 3 hours. The decoration process would have been shorter if it weren't for Mabel's attention to minutiae. However, Dipper and Wendy did admit that the Shack looked rather impressive with Mabel's decoration skills. Mabel put herself in position while the others summoned the children.

Wendy went up to the attic and woke up the kids.

"Aunt Wendy, what's going on?" Finn asked.

"There's a special surprise downstairs for you guys!" Wendy replied.

"Alright," the twins shouted in unison. They took a moment to awe at it. Phoebe trailed behind them unenthusiastically. She was still convinced Santa wasn't real.

When they came downstairs, Finn and Gladys immediately started playing in the fake snow while Phoebe looked around uncomfortably.

"Ho Ho Ho," said someone that sounded like he/she was falling down the chimney.

Mabel fell down the chimney ungracefully. She looked at her children and Phoebe. Finn and Gladys were bursting with suprise, whereas Phoebe looked as if she'd seen a ghost.

"Merry Christmas Finn, Gladys, and Phoebe!" You've been very good this year!" Mabel as Santa said.

Finn and Gladys were now gleefully smiling, giggling, and jumping for joy.

"I also have an elf and reindeer to show you kiddies!" Mabel said.

Dipper came out, trying to convince the kids he was an elf right away. It obviously didn't work on Phoebe, who recognized the face of her father. Waddles, dressed as the famous red-nosed reindeer, came through the doorway, and Finn and Gladys were completely sold on it.

"Onwards Rudolph" Finn and Gladys cheered while attempting to ride Waddles.

"What do you want for Christmas kids?!" Mabel cheerfully asked.

"Candy Santa! Candy!" Finn and Gladys screamed.

"The truth." said Phoebe.

"Don't be such a Scrooge," Gladys said, punching Phoebe's shoulder playfully.

"I'm not being a Scrooge, Gladys! It's not real," she shouted.

Gladys looked scared, causing Finn to run to and hug her. "It is Santa. He's real." Finn said.

"No he's not!" Phoebe shouted as she ripped Mabel's Santa beard off her.
Everyone in the room was silent and shocked for a moment. Finn and Gladys were left in shambles, their spirits and innocence broken. Once they excused themselves from the room, there was no other person to blame than Phoebe.

"How could you?" Phoebe angrily asked her aunt.

"I just wanted to make you, Finn, and Gladys happy." Mabel sadly answered.

"Well so much for that." Phoebe responded.

It was then that Mabel snapped. "Finn and Gladys are older than you and they still have that childlike innocence that you seem to be missing! You ruin everything with logic and science."

"Why is it so imperative that you make sure they still believe in Santa?"

"Because they need it!"

"Or is it because you need it?" She left the room after stating this.

Mabel didn't know what else to say or do except cry, now scared that her twins and niece hate her. She knew they didn't, but the fear still lingered. The words her niece said to her impacted her heavily. Was she making this up for her children's benefit or her own? She sighed, as if to neglect the obvious answer, but she consciously was aware of what it was. After about 5 minutes of crying and being hugged by her brother and sister in law, Mabel went to find the kids and apologize. She found them in the gift shop.

"Phoebe I'm" Mabel said before Phoebe hugged her.

"I'm sorry Aunt Mabel." Phoebe replied. The two shared a long heartfelt hug.

Phoebe was quick to apologize to Mabel, to Mabel's surprise. Finn and Gladys, on the other hand, were less quick to do so.

"Is Santa really not real," Finn asked, now able to look at his mother.

She sighed. "No, dinosaur, he isn't. He's more of an idea."

"So where do we get all those presents from," Gladys asked.

"You get them from us and people who care about you. Even if Santa's not real, you still get cared about, no matter if you're naughty or nice."

"Why did you say that he was real Mom?" Finn asked.

She didn't want to admit it, but she did it anyway. "I wanted you to stay young and innocent. Guess I went bonkers from it." She pulled both her children in a hug.

"I'm sorry sweeties." Mabel said.

"It's okay Mom." Gladys said as she and her brother and Phoebe mischievously starting tickling their mother/aunt.

"You crazy kids!"Mabel said while laughing.