Chapter 1

"What the – just what are you doing, Mabel?!"

The flat-capped, twelve-year-old boy was clearly perturbed by his sister's actions, despite the fact that he should have been used to her antics by now. Having come into the world only five minutes after her should lead to becoming comfortable with her many quirks quite quickly; however, 'comfortable' was not a word Dipper Pines would use to describe how he was feeling at this moment.

Mabel Pines, twin sister to the former, oddly nicknamed boy, was approaching her terrified sibling armed with an entire bag of sparkly makeup. Just behind the crazed preteen, were her trusty sidekicks who had been promised a chance to give the unfortunate boy a total makeover.

"Mabel! C'mon sis! Why are you doing this?!" Dipper cried out melodramatically, as his eyes darted around the twins' shared, attic bedroom in search of a path of escape.

Mabel didn't reply, a manic grin curling her mouth and exposing her braces as she and her minions only advanced menacingly.

"I'll do whatever you want! Just don't make me all glittery again!" The boy shut his eyes tightly and held his hands out in surrender. Mabel halted abruptly and her eyes lit up mischievously.

"Anything, bro bro?" the makeup bag in her hands fell to the floor as she straightened up, putting a hand to her chin as if she was seriously considering his offer.

After only a short moment of pondering, she swiftly crossed the remaining distance between her brother and stuck out a small, four-fingered hand. Dipper looked up hesitantly, and breathed a sigh of relief to see that she had abandoned her weapons.

"I'll figure out what you can do for me later, Dipping Sauce. But you got yourself a deal," she winked at her brother good-naturedly as he wiped imaginary, nervous sweat off of his brow and gave her a small smile.

He shook her hand…

and everything changed.

Mabel's smile grew unnaturally large and twisted, her pupils lengthened alarmingly, and her body began to expand rapidly, whilst her head, as if to contrast this sudden growth, narrowed to a point. By the time the unnerving transformation was complete, Dipper was staring aghast at the unmistakable form of the triangular psychopath, and dream demon extraordinaire, Bill Cipher.

And he was in absolute hysterics.

The two-dimensional demon was folded at the middle, literally doubled over with laughter, as he cackled maniacally, "It's not just funny anymore Pine Tree; it's actually getting sad to see just how dumb you actually are."

Dipper scowled, the shock of having seen his sister morph into the creature he hated most in the world wearing off as anger overshadowed his fear.

"What do you want, Bill?" He snarled at the triangle.

Bill straightened his bowtie and pulled a sleek, black cane out of nowhere, leaning on it as he responded, "Excellent question, Pine Tree! No really, it is; seeing as how you said you'd do whatever I wanted, and then shook on it."

The yellow triangle summoned the signature blue flames around his right hand, the hand that had been Mabel's only a moment ago, and Dipper visibly paled. Seeing this, Bill chuckled again, but this time it was more subdued, and much darker.

"Oh the fun we're going to have together, Pine Tree. I could make you my slave, erase your memory, make you destroy Gravity Falls for me…oooh, now that's a good one…"

The floating dream demon shuddered with pleasure as he rambled on about the several terrible things he could make Dipper do, while the poor boy could only quiver in his sneakers. There was no way out of this one. That little fact, he knew for certain.

"But," the demon had finally finished his twisted monologue, "I must confess Pine Tree; I've had something in mind for you long before this lovely encounter."

His eye narrowed gleefully in what was clearly a smirk. Dipper gulped, he definitely wasn't liking this. The evil dorito continued, "I'll be taking a little vacation and I need someone to replace me temporarily…"

He didn't need to finish his proposal for Dipper to understand what it was he was asking of him. The preteen's jaw hit the floor and he finally found his voice, "So, let me get this straight – you're asking me to do your job as a dream demon?!"

Bill cackled, "Temporarily, kid. And you wouldn't be a demon per se, you'd just look like me, respond to summonings, and have a few of my minor powers. You'd still be totally physical and essentially human. I'll still know when you're messing up, and will step in to take care of the actual deal making after I'm – well, you're – summoned." His eye narrowed so much as he laughed his distorted laugh that it was almost shut completely.

Dipper couldn't hide the fact that he was quite relieved at the yellow triangle's request. He wasn't going to enslave him, make him go insane or make him do anything illegal; it seemed almost too good to be true. Surely he, the other half of the Mystery Twins, could deal with a few summonings.

Clearly able to detect this relief, Bill sobered up immediately and grew almost double his size in order to intimidate the feeling out of the boy.

"Don't get me wrong, Pine Tree," his voice was lowering in pitch, "You won't see it now, but there most definitely is something in it for me."

Dipper clenched his teeth and merely nodded, wide-eyed. Almost immediately, the two-dimensional pyramid shrunk down to his normal size and threw a pitch-black, noodle-like arm around his shoulders, "That's my boy," he winked; or rather, blinked.

Dipper shuddered at the unwanted familiarity from the demon, only to realise that he, as well as what was left of the attic they'd occupied, had totally vanished. Dipper was left in a blinding whiteness that confirmed his suspicions. The whole thing with Mabel had been a dream, which was where a Dreamscape-dweller like Bill would be in his element.

Dipper face-palmed as he felt himself beginning to wake up. Stupid Dipping Sauce. Or, to be more accurate in light of his soon-to-be new situation, stupid Pine Tree.

Dipper

I woke up in my normal bed, in my normal attic room, in the nor – well, the Mystery Shack. I, however, was the only abnormal thing in the entire equation. I felt it the moment I opened my eye. Emphasis on the singular. The sudden lack of a whole other perspective woke me up as effectively as a cold bucket of water to the face would have. That, and the fact that Bill had suddenly decided to make his presence felt in the form of telepathic communication. (When did that happen?)

I forgot one thing Pine Tree, I rolled my eye, of course he did.

No need to be sassy now, he let out a snort of laughter, I just wanted to tell you that you can't tell anyone that you're you and not me. Capiche?

I groaned out loud, and cringed at how much like Bill the timbre of my voice had become. I thought back a silent yes, feeling like an idiot for doing so, and tried to climb out of my bed. It was then that I realised I wasn't in my bed to begin with. Instead, my now triangular figure was floating a few inches above it.

And, what was even worse than that realisation, was this next one. Sitting up in her own bed, gaping at me with an odd combination of surprise and horror on her face, was my twin sister.

"Oh! Oh, Ma – uh – Star! What a pleasant surprise!" I cringed inwardly at my goof up, but I couldn't tell her who I really was. If I did, then who knows what that crazed dorito would do to her? No way was I letting Mabel get mixed up in this mess I'd gotten myself into. My new, 'Bill' voice was also really unsettling me. It was disturbing to hear my words come out of Cipher's – whatever he had for a mouth – almost like it was me who had taken over his body. Which, I guess, had sort of happened.

"You're – B – B," Mabel stuttered a horrified greeting. This was honestly the first time I'd ever seen my sister at a loss for words. It was actually pretty funny. I started to chuckle, but quickly cut myself off.

What is with you, me?! This is no time to be laughing! Unless those 'minor powers' came with some limited edition, 'Bill'-brand, psychopathic side effects. Oh yeah, that would be just fantastic.

I felt a scowl spread across my features, and I clearly must have looked pretty dangerous, because Mabel let out a squeak and scrambled off of her bed. Her pillow fell to the floor, raising a rather impressive dust cloud from the wooden floor that clearly hadn't been cleaned since the Dark Ages. The dust, twinkling in the light from the morning sun, engulfed me mercilessly and I felt a familiar reflex building up as I was forced to scrunch up the area my nose would have been. I must have been a sight to see, the world's most dangerous entity with his eye half closed and polygonal form hunched over in order to gear up for something as mundane as a sneeze.

Unfortunately, I only realised what this meant for both me and Mabel when it was too late. I wouldn't have been surprised to find out that my sneeze sounded like garbled, backwards speech but what actually came out really did shock me to my core.

It sounded…totally normal. A delicate squeak was released from my new frame as I rubbed at where my nose should have been, trying to relieve that ticklish feeling that lingered after a good sneeze. When I registered the sound I had made, I froze mid-rub. I looked back to where Mabel had pressed herself against the wall, only to see that she was standing and that all traces of fear had disappeared from her face.

"You sneeze," she began in awe, "like a kitten."

She knew. Mabel knew that I was me. But what did I think, that I could have actually hidden it from her?

She started approaching me, and I tried to make myself look as unlike the real me as possible. I puffed out my chest and, on a whim, imagined Bill's black cane in my hands. I just managed to hide my surprise when it actually popped up in that exact position and leaned on it, mildly relieved when I saw Mabel start at its sudden appearance. In conjuring it up though, a thought suddenly flitted into my mind. Bill had said that I couldn't tell Mabel I was me. He hadn't said anything about her figuring it out on her own, did he?

Huh, maybe this new, distinctly 'Bill' way of thinking was useful for something after all. Like finding exploitable loopholes in deals, I thought as a smirk made my eye narrow slightly.

Mabel continued to approach me slowly, in spite of the cane's sudden appearance.

When she was still a safe distance away from me, she stopped and simply stared. After a few moments, I cleared my throat awkwardly. Still nothing. She was staring hard at me, as if waiting for something to happen.

Jeez, I forgot how intense my sister could be sometimes. I reached up with my left hand to rub at my forehead, where my birthmark would have been, like I do when I'm feeling particularly uncomfortable. Needless to say, I rubbed my head quite often.

The moment my tar black hand reached my triangular point, Mabel let out a screech that sounded worryingly like some kind of war cry, before lunging at me. She gave me such a fright, that I actually dropped the cane, which simply remained levitating in the position it had been in when I had let it go.

Bill had said I'd still be totally physical, seeing as I wasn't actually a demon. Well, the way Mabel crashed into me, and tackled me to the floor of the attic certainly proved that fact to be true. I felt all of it.

"What the HECK, Mabel?!" I yelled at her. I was angry. Angrier than I'd felt in my life; and for absolutely no valid reason. I felt my form enlarge, and had seen it happen on Bill enough times to know that my eye, and body, was turning a vivid shade of crimson.

My sister, the weirdo that she is, didn't even flinch. She simply crossed her arms over her chest and lifted an eyebrow at my overreaction. That took all the bluster out of me. I shrank to my original size and took a deep breath, holding it until I was sure I was a placid, unintimidating yellow again.

"I think I should be asking you that, bro bro." She had a point there. I looked down guiltily, but couldn't but help feel joy swelling in my chest at the fact that we'd found a way around Bill's deal. I didn't need to do this alone after all.

I scowled at Mabel as she snorted with unattractive laughter. Honestly, I pour my heart out to her while recounting all my plights from last night and she laughs at me.

"I'm sorry, Dipper," she wiped a tear from her eye, "But out of all the weird things to happen to us at Gravity Falls, I never thought that I'd end up having a tortilla chip for a twin brother."

I huffed and looked down at the floor angrily. Mabel and I were sitting cross-legged on our bedroom floor – or at least she was. It was surprisingly easy to get used to my new, two-dimensional, mildly demonic state; for both me and Mabel; and I had decided to stop trying to get my weird limbs to touch the floor.

My ever-optimistic twin suddenly clapped her hands together decisively and looked me in the eye with an expression more solemn than I'd ever seen her put on in our lives. Jeez, talk about mood swings.

"So, Dipperito," I cringed at the nickname, "Just what kind of mind-blowing powers did you inherit from Bill?"

"Can you please not say 'inherit' and stuff like that?" I face palmed my response, "He was already being way too weird with the fatherly speak last night. I don't need you doing it too."

Mabel gasped and her pupils dilated as she cooked up a scenario in her over active imagination.

"What if you are his son?" she began, "And, like – that's why he gave you his powers…so that you'd remember your life with him before?"

I cringed again at her line of thought, the whole situation was way too close for comfort with my current appearance to be funny.

She continued, undeterred though, "You must have been in a lot of danger for him to pass you off as my brother for all these years. But now, the love of a father for his son will finally win against all the odds stacked against them!"

She finished with a wild fist bump, and I could practically see the American flag fading into view behind her. She looked at me expectantly, but I only grimaced at her as best as I could with my only facial feature being one, oversized eye.

"Too soon?" she cocked her head at me.

"Too soon." I confirmed with a blink.

"Right. Sorry, bro bro!" she punched me where my shoulder would have been, and I rolled my eye.

"Whatever, Mabel. It's fine," I said, but I stopped with the scathing look and let my arms fall to my sides from where I'd had them crossed angrily over my bowtie.

She took this all in her stride however, as she does, and continued to prattle on about discovering my powers. I didn't really pay attention to her though, 'cause a weird feeling had suddenly materialised inside of me. It was like a weird, central tugging; and I didn't know what to make of it.

Just as I was about to say something about it, it suddenly intensified and I felt like my whole body was being pulled out of shape. I felt like laughing, screaming and crying all at the same time, so odd was the sensation. I was trying to figure out just whether or not it was actually painful, when the feeling disappeared all of a sudden. It had dissipated even more abruptly than it had begun.

I opened my eye, which I hadn't realised I'd closed, only to find myself not in the attic of the Mystery Shack anymore.

Instead of the dusty, but admittedly homely wooden room with my weirdo sister in front of me, I was surrounded by cold, grey brick. I let my gaze wander over my new surroundings only to find that they didn't get much more promising, at all. Every opening in the walls was barred with thick cylinders and the only door was made of a heavy, metal amalgamate with a single opening near the floor, that was also covered by bars.

The floor was cracked stone and stained with I-don't-even-want-to-guess what, and had clearly been housing insect colonies for decades. In fact, the only thing that looked even remotely new was circle of chalk with weird, but familiar symbols contained within and…

Oh.

A crudely drawn, but unmistakable Bill Cipher was in the centre.

I had just arrived at my first summoning. Whoop-dee-doo.