"If there's one thing you're right, Frida, it's that Hilda shouldn't have moved to Trolberg."
Frida jolted from her bed to see her entire room has turned gray. She wondered how did this happen.
"Up here," the voice said, and she noticed the source. It's a floating triangle with arms, legs, one eye, and wearing a black top hat and bow tie.
"Wh-Who are you?" she asked with fear on her face.
"Don't be afraid, child. My name is Bill Cipher, but you can call me Bill. Everyone does it," the triangular entity introduced himself.
"I'm Frida. And what are you doing here in my room?" Frida asked after introducing herself in return.
"I'm here to help you become the person you always wanted to be... perfect," Bill snapped his fingers to reveal a book, and he lets it float below her hands so that she can get it. Upon opening the book, she recognized the object.
"This is the book I was looking for!" she exclaimed before realizing, glaring at Bill. "So it was you who stole my book! If only I'd known this, then..."
"You're right. You're right," Bill extends a hand to stop her from attempting to make an assault on him. "I did it for one reason only: so that you'll finally understand that Hilda shouldn't have moved to this town," he continues on as he got closer to Frida. "If only she continued living in the wilderness outside Trolberg, you wouldn't be in a situation that she can't promise to help fix it. I can make things better for you. All you have to do is accept my cooperation."
As he extends his hand towards her, Frida looked hesitant. Deep down, she knows she shouldn't make deals with this entity.
"Tell me, Frida. Why did you trust that Hilda girl in the first place?" Bill asked when he noticed her hesitance.
"Because she's my friend," was her reply.
"Exactly. She's your friend. You helped her, you trusted her. And what has she done for you in return?"
Upon hearing the question, Frida is in her thoughts as she tries to think of an answer.
"Well she..." she tries to come up with something Hilda did for her, but she has a hard time thinking of it.
"Bingo! You don't have an answer, Frida," Bill took an opportunity to tempt her further. "For someone who claims to be your 'friend', she sure hasn't done a lot for you. Well, except nearly getting you killed over and over again."
"You're right, Bill!" Frida said with anger on her voice that could match with the fire from her eyes. "I did everything I could help her in our adventures, and what has she done for me in return? Nothing! Nothing, but getting me killed over and over again, especially with the ghosts!"
"So, are you ready to accept my offer?" the triangle demon extended his hand once again with a gleeful expression.
"Yes, I am!"
Frida shook his hand, having accepted his offer.
"So... what happens next?" she wondered as nothing else happened after the handshake, aside from the fact that their hands were in flames.
"This!" Bill suddenly pulls out her soul from her body.
"What the...? What is this?!" Frida is horrified to see that she has been pulled out of her own body, and that she now exists as a spirit. "What did you do to me?!" she examines herself as her hands phased through from the matter of her nature.
"Simple, I pulled out your soul from your body, and I possessed it," Bill replied, now possessing her body.
"You're crazy!" she cried.
"I sure am. You get that just now?" he grinned through her face while playing around with his new body, playing around with her hoodie ropes and the actual hood. "Wow, it has been so LONG since I've possessed a body. Woo! I feel like a new demon!"
"Why are you doing this?! I thought we had a deal!"
"Well, you can be perfect all the time when I'm in your body, and I have big plans for myself. Of course I have to make sure no one else will throw a monkey wrench into my operations, not even that Hilda girl."
Just then, a Nisse shows up from under the bed.
"Ah, I just need to take care of this loose end first," Bill grinned.
"I gave that book to you and released you from your imprisonment as you requested. Can you send me to a better place of my dreams in return?" the Nisse said.
"Sure, kid. I can take you there," Bill patted the creature's head for a few seconds before putting his hand on its throat. If that wasn't enough, he's actually strangling it.
"Bill, what are you doing?!" Frida becomes horrified to see what he's going to do to her Nisse.
"Getting rid of a loose end, that's what," was his reply, and the sound of his voice looked ominous when he said the line. "I take him by the throat, and squeeze, and squeeze, and squeeze until he foams like a dog. And then squeeze some more," the Nisse is practically foaming at its mouth. "And when the eyes are about to pop out, squeeze just a little more."
When its eyes are popping out from its hair, its neck snapped. Bill has murdered a Nisse, and Frida is left horrified from this action.
"You killed a Nisse!" she exclaimed.
"I sure did. AHAHAHAHAHAHA!" he laughed maniacally, showing her that he really is crazy. "Oh, just a precaution. Now that I'm here, this book has to go bye-bye! AHAHAHAHAHAHA!" he started ripping the very book that costed her friendship with Hilda and David to pieces before placing them in a trash can where he makes a bonfire out of it. All the while Frida herself is left in horror to do anything about it. While she tries to use her wrestling moves on him, it didn't deal him any damage. "Give it a rest, kid. As long as you're a ghost which is ironically the very creature that costed you your friendship with that girl and that boy, you can't interact with this world. Not as long as you have a vessel which I doubt you have one here."
This is a worst day for Frida indeed, and the next day to come upon hearing the news of the weather from her radio.
Author's Note: What do you think of my first Gravity Falls and Hilda crossover fanfiction story? It would great if Bill Cipher, the main antagonist of the former, is also the main antagonist of the latter. Imagine what would that be like.