Dipper couldn't believe it.
Pacifica, one of the new arrivals in town for the summer who he had met one morning while reading after she tripped over his foot and literally ran into him, had asked for his help to get her cousin back. When she explained what she had heard in the woods and how they had disappeared, asking Dipper if he could find the mysterious Northwest girl, he immediately led her to the Northwest mansion up on the hill. This whole ordeal shocked him just that much more because he and Mabel were also half-siblings. His dad had divorced her mom and went bitter, always pressuring Dipper. Dipper and Mabel were born around the same time to different mothers. Priscilla divorced Bud when she found out he was having an affair with another woman-his mom-who became pregnant. But she was pregnant, too, and remarried to Preston Northwest, raising Mabel as a Northwest child. It was kind of confusing, so he didn't think about it often.
Dipper didn't bother with pleasantries. He threw open the doors and marched right in, Pacifica in tow.
"Mabel!" He called, voice forceful. No response. He growled in frustration. Then he turned and marched up the stairs. He walked through the halls with skill having long ago memorized them. Pacifica stumbled along behind, not really sure where they were going.
"Umm, Dipper? Where are we going?" She asked nervously as they passed a room full of creepy stuffed animal heads and bear-skin rugs. A ridge of the floor in there stuck up at one side like someone had dragged an axe through it. Maybe someone had.
"Her room." He replied, simply, voice deep and angry. Pacifica said nothing more after that.
Finally they reached the end of the hall. A door was cracked open at the end, light spilling out and pooling in front of the door. As they neared, voices could be heard.
"You're crazy!" the voice was male and cracking with distress. Pacifica gasped and cupped her hands over her mouth.
"That was Bill!" She hissed to Dipper. The boy glared at the door like he was locked in an intense staring contest with it and stopped in front of it, listening.
"Oh, come now. I'm not so bad. All you have to do is say you like me." The sugary voice that Dipper know so well followed. It hurt to hear her saying that. So it was true. She really had kidnapped Bill.
"What!? Why would I do that when you tied me up and hid me in your room, you psycho?" Bill snapped. Dipper and Pacifica peered through the door and saw Mabel standing before a rope-bound Bill, finger under his chin, tipping up his head so he would look at her straight. His golden eyes smoldered with anger, but the fear was like a wet blanket over his fire of defiance.
"Hm, cute." She jerked her finger up, flicking back his head and walking around him like a hunter surveying their next catch. Dipper couldn't take it anymore. He burst through the door and marched up to a startled Mabel, brown eyes flashing with fury and betrayal. "D-dipper!" She squeaked, having the nerve to step in front of Bill to hide him.
"Mabel, what are you doing?" He demanded, stopping before the girl. "This isn't like you, you need to stop!" Mabel's eyes flickered with a mixture of fear and anger much like Dipper's.
She hung her head, glaring at the floor. "Because no one likes me when they get to know me. And I just really wanted someone to like me…" She whimpered.
"So you thought kidnapping someone and making them like you was the answer?" Dipper gestured to Bill in exasperation.
Mabel looked up at him, eyes sad and watery. She couldn't answer him at all, not justifiably.
Then Pacifica walked in, her eyes darting around, nervously.
"Pacifica!" Bill gasped.
"Bill!" She ran over to her cousin and started untying him while Mabel backed away, standing off to the side. She shot the girl an angry look as she straightened, helping Bill up. "Are you okay? Are you hurt?" She started checking him swiftly. He laughed a little as she found a ticklish spot.
"I'm fine, Paz. Everything's fine." He assured her. She gave a puff of relief. But Mabel clearly wasn't done with her anger.
"You all suck." She growled. Then she snapped her fingers. A butler rushed in and she looked fiercely at him, fury blazing cold and dangerous in her eyes. "Initiate." She hissed. The butler nodded, then turned on the children. His eyes glowed red and he moved into a battle stance, assorted weaponry activating and sliding out of metal hatches. The man's movements became semi-mechanical.
"H-he's a r-robot?!" Bill gasped, stumbling back and tripping over his abandoned ropes.
Mabel chuckled darkly, dangerous glint never leaving her eyes. "Yes. Preston never pays close enough attention to me to notice when I sneak in my little defensive measures. The bastard's never cared for me, anyway." She absently picked at non-existent dirt from under her nails. She flicked her wrist at the robot. "Destroy them." She spoke calmly and carelessly, like it was no big deal she was having her relative and two new comers torn to shreds.
The robot advanced, machinery whirring as weapons kicked into high gear.
"Mabel! You can't do this!" Dipper cried as he and the two others were backed into the wall. Nowhere left to run. "I'm your brother, for peat-sake!"
Mabel growled. "Half-brother! Our father was an idiot. He never did anything right and that includes parenting. He treats you like dirt and we both know it. So I'm going to put you out of your misery. You'll thank me later." Her voice began furious, but faded to a smooth, cool tone.
Dipper's brain moved a mile a minute. He grabbed a book from his jacket, which he threw on before leaving his house, and flipped through the light caramel-colored pages, searching for something. Finally he found it.
"Guys! Grab my hand now!" He yelled over the whirring of the machines. Bill and Pacifica didn't question. Bill grabbed Dipper's hand and Pacifica his wrist. At first the chanting of the ancient language sounded strange. The Pines kids thought Dipper had gone crazy or something and started rambling gibberish. But then, in a flash of white light, they all vanished. Pacifica yelped. Bill screamed. Dipper chanted. Then they were gone, leaving a scorch mark on Mabel's bedroom floor. The butler returned to its normal mode and Mabel was left staring dumbfounded at the place where the three had disappeared. In their place was a note, as well.
She lifted it and looked at the words. They were in Dipper's handwriting. It's over, Mabel. You can forget about being friends ever again. Have a nice life. –Dipper Gleeful
And in that moment, she cried a little. The girl's previously unbreakable emotional barrier crumbled and she was alone once again, this time entirely. Her only true friend and relatable relative was never going to visit her again, and it was all her fault.
A/N: no, Mabel doesn't really come up much more in the story. She's a jerk in this dimension, so no one else will be friends with her. Sad I guess, but she asks for it.