Mabel burst through the front door, Soos and yourself trailing behind.  "Dipper!  We've gotta help Stan!"

The lanky teen stopped sweeping the floor and gave his sister a questioning look, adjusting his blue trucker hat. His confused eyes were the warm color of melted chocolate, matching the messy locks of hair cascading over his forehead.  "Wait, what?"

Soos tried to explain what was going on in between his Burrito Bites. "This evil triangle guy said he's gonna break into Stan's mind and steal the combination to his safe! Also we stopped for snacks on the way here."

Your heart stopped as you heard those words. You made the time-out sign with your hands. "Triangle guy?!"

Dipper noticed you for the first time and crossed his arms in contempt. "Mabel, who's this?!  And why's she wearing Robbie's hoodie?!"  He spat out the name acidly. 

Mabel suddenly seemed very interested in her sweater sleeve. "It's, uh, Y/N. We met at the grocery. She gave Soos her snack and said she might be able to help.  As for the jacket..."

You crossed your arms.  "I got this through mostly legal means, it's not the angsty emo boy's anymore." 

Her brother narrowed his eyes and scowled, pushing up the sleeves of his own navy hoodie. "Let me get this straight: a complete stranger gave you one bag of Burrito Bites, and suddenly she can be trusted with our family's secrets?!"

Dipper's voice raised to a shout on the last word, and Mabel winced subconsciously. "We need all the help we can get. Stan's in danger."

Dipper raised an eyebrow and glanced at his sleeping grunkle. "Seems safe to-"

Suddenly, the temperature in the room dropped ten degrees. A deep cold pierced your bones, and you knew without a doubt you were in the presence of something fundamentally evil. As you watched, a shadow twisted around the room, forming the silhouette of a young man, with a hole were the right eye should be. He smiled with pointed teeth, tipped his hat, and dove straight through the old man's forehead.

Stan, still deep in slumber, cringed and started kicking in jerky movements. "Gah-!"

"I'd classify that as "danger," Mabel whispered, eyes wide.

Dipper unzipped his jacket and pulled out something from a specially made pocket: a large leather bound journal. It's faded maroon cover clashed against a golden six-fingered hand on the cover, giving the impression of something truly ancient. The book didn't look like anything at all, but he was so careful, almost reverent with it, there had to be more to it than reached the eye. The taller twin opened up to a page showing an ink sketch matching the demon we had just seen. "Beware Bill, the most powerful and dangerous creature I've ever encountered. Whatever you do, never let him enter your mind."

Mabel grabbed it from him, showing none of the respect Dipper had. "It is possible to follow the demon into a person's mind and prevent his chaos. One must simply recite this incantation..."

Her brother snatched it back in irritation. "I don't think it's a great idea to read it aloud before we're ready." Dipper ran into the kitchen, coming back with an armful of candle stumps. He crouched down and began to arrange them in a circle around his great uncle, muttering to himself.

You leaned towards Mabel. "I thought you said Stan was the crazy one."

"I'm OCD, not deaf," Dipper muttered.

Mabel shrugged. "Just let him do his thing."

He turned off the lights and lit the candles one by one until the room was illuminated with ghostly light. "I spend all day cleaning sinks and fighting bats for Stan and now I have to save him from some crazy brain demon?"

You gave Mabel a look, but she shook her head. Later.

"Get ready, guys. We're about to journey into the most horrifying, disturbing place any of us have ever been: our uncle's mind."

Your hands clenched into fists in irritation. You had pulled countless all nighters, put your physical and mental health at risk to find the demon for nothing.  That rickety journal had an idiot-proof guide to both summon and banish him, and there was no way you were letting this opportunity slip through your fingers.  "Let's do this."

Dipper seemed shocked, but covered it quickly.  "You aren't going."

Your mouth twisted into a wry smile.  "Nice try.  I know just as much as you do, maybe even more.  I'm tangled up in this whether you like it or not." 

He grit his teeth as he mulled it over, trying to find a loophole in your words.  Finally, he sighed in defeat.  "Fine.  But know I don't trust you."

"You don't need to, I don't trust you either."

"Fair enough." 

Dipper grudgingly held out his hand, and in the candlelight his gaunt face seemed skull-like.  You reluctantly took it and held Mabel's hand while she took Soos's. The poor guy had been silent the whole time, terrified by the events he had witnessed. 

Mabel let out one final breath to calm her nerves.  "Let's do this.  For Stan."

Dipper grimaced at the last part but put his hand on his uncle's fez.  "Videntus omnium.  Magister mentium.  Magnesium ad hominem.  Magnum opus.  Habeas corpus!  Inceptus Nolanus overratus!  Magister mentium!  Magister mentium!  MAGISTER MENTIUM!"  As he shouted the last words, you felt your spirit slip out of your body and into Stan's mind. 

You cracked your knuckles in the colorless void you had arrived in.  Wherever Bill Cipher was hiding in this mess, he'd better be ready.  Y/N L/N was coming for him, and she wasn't going to show any mercy.