Here's the prequel I promised... It's kinda dark, and this one'll be taken from Mabel and Dipper's POV's

Mabel

A shape, a person; small and oddly bent, was lying there. I took a step forward and instantly recognised the orange shirt and scruffy brown hair. I rushed over and fell to the floor next to him. It was my twin, Dipper. But his face didn't look like anything I'd ever seen before. His eyes were closed and I gripped his shoulders, panic surging inside me.

"Dipper!" I screamed, shaking his shoulders, tears streaming down my face, "Dipper! Dipper, wake up!"

His bruised, swollen eyes slowly opened and looked up, unfocused. His face was black and blue, bloody and covered in ugly purple patches. What had he done-? And then my eyes wandered down and I found my knees were soaked in a thick red liquid. Oh my god, Dipper! A pool of blood bubbled and oozed from a wound in his stomach.

"D-don't worry Dipper!" my voice trembled, "You're gonna be a-okay!" I gripped his hand tight and stared back into his deep brown eyes, identical to my own, just as they began to slide shut again.

"I'm so… tired." he whispered. His voice was barely more than a croak and another wave of tears washed over my face as I watched by brother. My strong, unbreakable, determined brother totally beaten and unwilling to carry on.

"No! No you're not!" I cried, "Don't you dare fall asleep!" but it was too late. His eyelids met and his face relaxed. He was completely still, his chest frozen. He wasn't breathing!

"Oh my god, Dipper!" I yelled, squeezing his hands, "Help! Someone, help! Please!"

Dipper - earlier

My cheek burned, as did my swollen eyes, filled with tears. Bill slapped my face again and I felt the blow, but couldn't react. Then he slid the tip of the blade slowly along the fingertips on my left hand. Again, I felt it and wanted to scream, but I physically couldn't.

"Aww, this is getting boring." his voice laughed in my ears, "What else should I do for fun?" I watched as my own hands wiped the knife clean of my blood. I couldn't move, Bill had me and there was nothing I could do now but look as he controlled my body, like a puppeteer pulling on the strings. The only thing I was aware of was the pain coursing through me as I stared up at myself. I was like some kind of voodoo doll and Bill had bruised and tormented my frail, human body for fun but obviously, that wasn't enough for him. He wanted to see someone really suffer.

"Oh I know!" the words exploded from my mouth, in a voice that wasn't mine, "Wonder what your sister looks like, dismembered and hung upside down?" No! Not Mabel! Bill's laugh echoed around my head and as my body turned to walk away, a surge of anger grew and welled up in my throat. "Well, see ya-" My foot stopped in mid-air as I let out a cry and forced Bill out.

His power was useless unless he had a vessel, which right now, was me. If he couldn't get in or find a vessel, he'd be weak. Or better yet- if there were no vessels for him to take…

"Huh..? That's weird…" his voice pummelled at my throat, "I can't control my-" I forced my arm, gripping the knife, up to point at my own chest. I could feel Bill's panicked emotions running circles around my brain. Somehow, I could move again and he didn't understand why just as much as I did. I needed to scare Bill into leaving my body. Without me to carry his soul, he'd be powerless.

"What the-? Hey!" Bill cried, "What the heck are you doing?!"

I went to strike the knife into myself but Bill stopped it right in front of my eyes.

"You think I'm just gonna let you kill this vessel?" my own lips read the words in Bill's voice, "We made a deal!"

The knife was trembling in my hand. If I let him beat me, he'd use my body, my life, to do terrible things to the people I love. Starting with Mabel…

"Our deal is off!" I screamed, and my real voice shattered the silence. I plunged the blade hard into my stomach.

"Dipper!" I opened my eyes, "Dipper!" Whose voice was that? "D-don't worry Dipper! You're gonna be a-okay!" Mabel? I squinted up at her. She was knelt down over me, crying, a strange figure hovering to her left. What-?

Bill, in his true form, stared down at me. Out loud or in my head, I wasn't sure, he spoke.

"Did I win?" the triangle chuckled, before fading away as tears filled my eyes.

I closed my eyes again, "I'm so… tired."

"No! No you're not!" Mabel cried, "Don't you dare fall asleep!"

Her sweet voice faded and then I was drifting. Flying through my own thoughts, shrouded by guilt and pain.

"This is not over, Pine tree…" Bill drawled, "When you wake up, we'll continue where we've left off. And I will win…" Then, what if I never woke up..? Then everyone would be safe… Especially Mabel.

...

*sniff* sad...