What if Dipper and his clones found Lebam hiding in the closet? All characters belong to Alex Hirsh and Disney, not me.
Lebam the Party Crasher
Lebam, Mabel's mirror doppelganger, had been created by Gideon to do his bidding and be his short-term substitute girlfriend until he could have the real Mabel. She had escaped his clutches and saved Dipper's life the night Gideon tried to ambush Dipper at the Li'l Gideon merchandise warehouse, and since then Mabel had offered her a home and a secretly shared life.
Lebam knew there was going to be a party at the Mystery Shack that night, but she was comfortable where she was in the closet and saw no need to move. She still had a lot of her stash of Smile Dip and planned to get into it again. Even if party-goers wandered up to the attic they wouldn't find her easily.
The whole house was weird. Sometimes it seemed like there was more space on the inside than the outside. Due to some very clever technological trickery (holograms, she thought), the two hallways on either side of Mabel and Dipper's room couldn't be seen if you faced their door from the stairs. All you could see was one door in the blank wall. But if you backed in at the right places on either side, you found hallways with rooms off of them. On the left side as you faced Dipper and Mabel's bedroom door was Grunkle Stan's bedroom. On the right side was a large hallway with a coffin and assorted junk in the corner, a cluttered storage closet (Lebam hid and slept there), and a room with a secret ladder she sometimes used to sneak downstairs.
Lebam snuggled down in a pile of coats and opened a pack of Smile Dip. She expected an undisturbed evening. Unfortunately for her, she was wrong.
Lebam heard footsteps coming up the stairs into the attic. Two voices were talking, both sounding like Dipper's, but a little flatter. She could tell the difference only because of her sensitive llama hearing (due to fiber from a genuine llama-hair sweater being used in her creation, Lebam had llama senses and llama powers of digestion).
"Okay, 8, we're the advance team. It's our job to prepare the closet to make Dipper Classic comfortable while the others drag him up here. I've got the cheese and cracker snack."
"I've got the coloring book and crayons, 9. It's a little rude to rub it in that he's acting like a little kid, but seriously, just talking to Wendy like a normal person? He honestly thinks that's going to work?"
"Since he's not following the plan, it's up to us to do it for him, for his own good."
"But who will dance with Wendy instead? I think it should be me. Do you agree, 8?"
"We'll settle that once we've got Dipper locked up."
By the time Lebam realized it was her closet they meant, it was too late to get out. She climbed up to the ceiling of the closet and braced herself against the attic beams. The clones didn't look up as they placed the coloring book and snack.
Moments later, the other clones came in dragging Dipper. They pushed the coats aside and pushed him into the closet.
Dipper said, "No, wait! Ahh, I can't breathe in here!"
One of the clones said, "Yes you can! Plus there's snacks and a coloring book in there for you!'
Dipper sat down on the floor of the closet and angrily began to eat the cheese and cracker snack. Outside, the clones debated who should get to dance with Wendy instead.
Lebam was having a hard time maintaining her braced position. She shifted her weight and slipped a little, making a scraping noise.
Dipper heard. He looked up and saw her. "Mabel, what are you doing up there? I thought you were out there dancing, competing with Pacifica for the Party Crown."
Lebam dropped down and landed beside him. "I guess the jig is up. I'm Lebam, Mabel's mirror doppelganger. I've been living here secretly for a while."
Dipper recoiled. "A doppelganger?"
He consulted his Book 3. "Doppelgangers are the evil opposites of the person they copy. They aim to kill the person and take over their life."
"I'm not like that. I'm good. I saved your life from Gideon, that night at the warehouse," said Lebam.
"I don't believe you," said Dipper. "That was the real Mabel. I've got problems of my own to deal with right now, but I want you out of this house tonight, or everyone's going to know you're here."
"That's unfair," said Lebam. "Look, I'll let you out of the closet."
She used a hairpin and picked the lock.
"I could have done that myself," said Dipper.
"Not as fast as me," said Lebam.
"I'll give you a head start," said Dipper. "When I leave, all the clones will chase me. That's your chance to get away. If you do, I won't tell anyone you exist and that you were hiding here. Otherwise, I'll expose you, and fight you if I have to. I'm sure I can find your weakness in this book."
Lebam hissed at him. "You're mean, Dipper. Mabel will hate you for this."
"I'll take that risk, you monster. It's for her own good," said Dipper.
After Dipper and the clones were gone, Lebam slipped down the ladder to the museum, through the underground passage that led to the gift shop, and out the gift shop door. She took a few grape popsicles on her way, as fuel for the road. If Dipper didn't want her here, she was going to have to find a new home somewhere else.
As she walked out to the road, she found a very angry-looking girl sitting on a rock. The girl looked up at her.
"You!" she snarled. "This is all your fault, Mabel."
"What are you talking about? Do I know you?" asked Lebam.
"Do you know me? That's a... very good question," said the girl in a tearful voice. "You met Pacifica Northwest, queen of Gravity Falls society. But you haven't met me. I'm a copy of her."
"A copy?" asked Lebam.
"You probably think I'm crazy," said Pacifica's clone. "Did you know it was possible to make a copy of a human being?"
"I certainly do, and I believe you," said Lebam. "Tell me your story."
"After you danced so well and started getting applause, I... Pacifica was jealous. She headed past the bathroom to find a place to sulk and regroup. Then she saw your brother, Dipper, talking to a few copies of himself. He was taking them upstairs to plan how to ask Wendy to dance. She hid and they didn't see her."
"I see..." said Lebam. "Then what?"
"She found a strange copy machine in the room they came out of. She decided it might be useful to have her own clone to help her win."
"Did you help her?" asked Lebam.
"Once she saw me, she wouldn't let me do anything. She said I was colorless and faded, unworthy to stand in for her," said the clone. "I hid in the bathroom for a long while. When I came out, Wendy was there talking with your brother, waiting to use the bathroom. I stormed out and left the party. But now that I'm out here, I have nowhere to go... no life..."
"Join forces with me," said Lebam. "I'm just like you, a copy with no place to go."
"Really?" asked Pacifica's clone.
"If you look in the window, you'll see me in there dancing," said Lebam.
"Oh," said Pacifica's clone. "I have a little money on me, just two hundred-dollar bills and change. I spent one hundred-dollar bill on the fifteen-dollar exit fee to get more change. The money won't last long."
"We'll think of something," said Lebam. "And we can give your original a bit of comeuppance, once I call in an anonymous tip to the police."
Pacifica Northwest, wearing the Party Crown, was carried toward the exit door of the party on the shoulders of her friends who had been invited to an after-party on her parent's boat.
Grunkle Stan stood at the doorway. "Exit fee, fifteen dollars each."
"What a measly charge," said Pacifica. "Typical of a relative of that Mabel. I'll pay."
Her friends set her down and she produced three hundred-dollar bills. Stan took them and started counting out change.
There was a knock at the door. Sheriff Blubs and Deputy Durland stepped in.
"We have reports of someone passing counterfeit hundred-dollar bills," said Blubs.
"You oughta check the cereal numbers of the hundreds you took in tonight," said Durland. "I didn't know money was made of cereal, did you Sheriff?"
"It still wouldn't be as sweet as you, Deputy," said Blubs.
"Hey, wait a second," said Stan. "One of the serial numbers on the hundreds you just gave me is a match to the one you gave me before, Pacifica. You've been going in and out and milking me for change for phoney money!"
"I never did," said Pacifica.
"I have a security camera set up at the door for positive ID of everyone who goes in or out," said Stan. "And I know you're on it."
"That wasn't me. That was my clone," said Pacifica.
"That's what they all say," said Blubs. "You'll spend at least a night in the county jail. Cuff her, Deputy."
Pacifica looked around, but her fair-weather friends had moved off. She growled, "You'll pay for this, you and your whole low-life family."
"Your parents will have to pay me, later... for the exit fee. Bye now," said Stan. "Dress warm in jail."
Pacifica, in a short skirt and no sweater, shivered a little. They cuffed her and took her away.
"Now that I think about it, a whole bunch of kids paid to go in and out over and over, like that kid in the white hoodie and plaid pants," said Stan. "Rats, now I have to compare all the serial numbers of all the money I took in. This is going to take me all night."
Inside, Mabel partied with her new friends Grenda and Candy.
Pacifica's clone headed off into the woods with Lebam.
"My name is Lebam, backwards for Mabel. May I call you Acificap?" asked Lebam.
"No," said the clone. After a pause she said, "All right, I guess, it's better than nothing."
"Yay, Acificap and Lebam. We're going to be best friends."
Acificap sighed and nodded. "All we've got are each other."
As they went into the woods, young woman with a purple streak of hair on the right side of her face followed them.