Gravity Falls belongs to Disney, Undertale belongs to Toby Fox.

Prologue: Post-Apocalyptic State

Darkness. Nothing. Boredom. Bill. The triangular enemy of the Pines family. He had been so close. Then he was tricked into entering the mind of Stanley Pines. How could he have been so stupid. He would never have thought that Stanley would allow his mind to be erased. That was how he ended up in what he could only assume was death.

"Well this is boring." He spoke to no one in particular.

Of course, when one is a reality warper everything is boring if there is no reality to warp. And, unfortunately for the inter-dimensional demon, death was simply a reality that could not be warped. But oh how he wished it could.

"Well this is boring." He repeated.

"Indeed it is." A calm sinister voice, laced with evil intent replied.

Bill was quite surprised, he had not expected an answer in this inky black void.

"Who said that? I can make a deal with you. I help you, you help me." Bill called out to the mysterious voice.

"Bill, Bill, Bill. I would appreciate it if you would not beg. The Bill Cipher that I have been studying for the past season would not beg. Now, I am here on business...so to say. First I should thank you."

"Thank me. Why, I don't remember making a deal with you or helping you, and so how do you know me?"

"You did help. When you started your, so called, weirdmageddon, you broke me free from my prison. I simply re-entered the third dimension through the rift that you created. And to take a line from your book, I know things, LOTS OF THINGS."

"Ok, so why do you speak to me?"

"Two reasons. First off, you are an interdimensional reality warper. One of the most powerful reality warpers I have ever met. Unfortunately you are only interdimensional, existing in one dimension. Your full talents go to waste. I however, am a transdimensional reality warper. I exist in multiple dimensions, but I can be imprisoned in a single dimension. Which leads me to my second reason. Like I said I am here on business. I am going to make a deal with you. I know that You seek revenge, a physical body, power, and an escape from here. I can offer you that...however I would like something in return. I am in need of an...emissary so to speak. Unfortunately only a small part of me was able to escape into the third dimension. It latched on to you. Now I am speaking to you and offering my deal. Accept or decline, the choice is yours."

"OK, blank face. First off I don't even know who you are or what you look like. Secondly how do I know I can trust you?"

"To answer your second question, you can't. I can even turn it around and ask the same thing of you, Bill Cipher. I know all about your betrayals in the town of Gravity Falls. You must realize that I have been trapped in a dimension directly connected to the falls far longer than you. As for what I look like, that will be revealed in due time, and you can call me Hedron."

"What is that like a nickname or…"

"That is my last name and what you will refer to me as. Now do we have a deal?"

"Yes."

Bill wreathed his hand in a blue fire to shake hands and set the deal. Out of the darkness came another hand. This one was more skeletal in nature and was wreathed in a purple flame. Bill reached out and shook the mysterious hand.

"Now then. Bill Cipher, I charge with preparing the way for a new reality. This portal will take you back to the third dimension. Be warned some time will have passed since you were defeated. How much is unknown."

As Bill shook hands with Hedron, a swirling black and white portal opened up. Bill didn't hesitate to leave. After all, a reality warper is bored when there is no reality to warp.

"Yes, go and prepare a way for a new reality. Prepare a way for me. PREPARE A WAY FOR THE TRUE DARKNESS OF GRAVITY FALLS. THE WHOLE WORLD WILL TREMBLE BEFORE ME. AND YOU SHALL BE THE FIRST TO FALL, BILL CIPHER."

So this is a little idea that I have bouncing around in my head after reading a few of the Gravity Falls fanfictions on the site. I recently read Brothers-The Origin of Bill Cipher by TheReturnToTheFalls. I liked the idea of Bill not being dead after he was erased from Stan's mind. So I kind of copied that. Shortly after reading that story I started thinking of this conversation between Bill and my OC who's last name is Hedron. This story will be more of a side project for now. I would like to fully complete the Hollows of Remnant before getting too deep into this one. I might update now and then or whenever I get inspiration for this story.

I am thinking of making this a crossover but I am unsure what to cross it over with, so for now it will remain as a one universe story. If you have any thoughts please leave them in a review. As always, until next time I tip my hat to you.