I'll finish and post it in One Shots later...

Dipper was angry. Really angry. The only time he felt remotely close to having this much rage was 13 years ago, when he found out his great uncle had all the secrets to gravity falls hidden almost literally under his nose.

Dipper gripped the knife he had on his belt and slashed it towards Bill's neck. The human-disguised demon dodged. "Come on Pinetree, I know you couldn't cut me no matter how hard you tried."

Dipper threw the knife at the demon, he missed drastically. He growled as he sprinted towards the demon, tackled him, and pinned him to the ground. "Spill your guts demon." He said in almost a hiss.

"Did you not like your gift, sapling?" Bill teased. "I thought you'd appreciate a little power."

Dipper's eyes flashed red, he gripped his hair, still sitting on Bill. He screamed as his canines turned to fangs, his nails grew significantly sharper. He grabbed Bill's wrists and held them down, stabbing them in the process. "Change. Me. Back." He hissed.

"Now why would I want to do that? Tell me, Dipper." Bill said with a shit-eating grin.

A small whine escaped Dipper through his angered, barred fangs. His eyes flashed again and he growled, digging his claws deeper into Bill's skin. "Don't you try to charm me, you shit eating monster."

"Says the clawed and fanged creature pinning down a what-seems-to-be-human." Bill smirked. "And plus, what would harming me accomplish?"

Bill's smirk faltered as Dipper smiled unnaturally. His mouth would've had to been torn for him to smile more. He put both Bill's arms above his head and held them with one hand. His other clawed hand ran down Bill's cheek. "Sso many thingsss." He hissed, flicking his claw at the demon's skin, cutting through and leaving a thick scratch on his face, the blood dripping down the side of his face.

"Maybe a puppy wasn't so bad of a present idea, huh Pinetree?" Bill said, looking left and right to see if there was anyone nearby. Nope. With a snap of his fingers the demon was teleported a few meters away, standing. He would've gone further if the body he inhabited wasn't such a terrible conductor, like he assumed Dipper's.

13 years ago when he possessed the kid, he couldn't conduct jack-shit. Now he was overflowing and conducting it left and right, mostly changing his appearance. What had changed?

He was snapped out of his thought almost immediately and began running- no, sprinting to the shack. "Shooting Star! Stanford! Get the power disabler!" He yelled. When the shack got in sight.

Grunkle Stan and Mabel were cleaning up after the twins' birthday party. Everyone had just left and they were wondering where Dipper and Bill went... until now.

Mabel pulled it out of seemingly nowhere. "Uh, ok... why?" Her question was answered by a roar, similar to the ones in Jurassic Park, and a figure emerging from the woods. Bill ran to Mabel and hid behind her.

Dipper's eyes were glowing red, his skin and clothes turned to an inky black, a smile plastered on his face as he drummed his claws together. "Mother of man monkeys! Forget the disabler! Get the shotgun!" Stan yelled.

"You may not want to shoot him, I mean, try if you must, but I can see a few minor flaws in your plan" Bill commented.

The dark figure sprouted black liquidy wings. "Bill! What even is that! Where's Dipper!" Mabel yelled.

Dipper bat his wings once and flew full speed at the crowd. "Shit, everyone inside!" Bill yelled, pushing them through the door into the shack. Everyone panted from the rush.

"Bill!" Stan yelled, getting ready to strangle the demon's vessel. "What was that, and why would you lead it here?!"

"Well, that certainly is a funny question where the answer to said question, is hilarious." Bill started, but was interrupted by knocking on the door. "I wouldn't open that door no matter what." He commented blantly.

The knocking became aggressive. "Guys! It'sme letmeinletmein!" Dipper yelled from behind the door, the others could hear him choking up.

His sister ran to the door, getting ready to slam it open. Bill stepped into her way and repeated his earlier statement. "No. Matter. What. Shooting Star... then maybe I'll reconsider telling you what happened."

"Dipper's out there!" Mabel yelled.
"And we're not going to wait for him to get killed." Stan added.

"One. That's why we're in here. Two, that was exactly my plan Stanford." Bill laughed. "Unless Shooting Star here wants to use the magic disabler."

"Wait..." Mabel gently pressed her finger to her own lips. "Use it on Dipper? Why? He doesn't have any magic." Mabel said.

"That's where you're wrong, shooting star." Bill grinned. "Here's that funny story I was going to tell you, for the little tree's birthday, I thought I'd give him a bit of magic... but it would seem, he's a conductor with no control now. So-"

"Why would you do something like that? Who just gives powers away willy nilly like that!?" Stan yelled.

Ignoring Stan, Bill continued. "Ahem, so, we need to stabilize him by disabling his powers."