Prompt:If Bill were able to convince older!Twins to make some kind of deal with him for dream demon education (secrets of the universe, infinite cute sweaters, etc) would he wind up, intentionally or not, being a corrupting influence?

It's Paved with Good Intentions

At first, no one thought it would become that much a problem.

No one seemed bothered when the first signs started cropping up, either, come to think of it.

Dipper was surprisingly nonchalant, saying he could stop any time he wanted too. Mabel was the more realistic of the two, in that she commented simply didn't mind. And Dipper had always been a bit more impressionable than his sister, in all honesty. Soos didn't notice. Wendy neither.

Even Stan seemed okay with it.

Which, really, should have been their first clue something was seriously wrong. Or at least headed in that direction.

The Pines twins had made a deal with a devil, you see.

Not a very bad one. Nothing as crazed ad that twerp Gideon's had been. There's was an innocent, hopeful, do-it-for-the-greater-good sort of deal. But it was a deal nonetheless. They only wanted to know secrets and tools of trade for what it meant to be a Dream Demon. In return, Bill was with them always. He had things he wanted, of course. Like soda, sweaters, a little nest on Dipper's bedside table he could curl up in at night and get some rest. He was given automatic access to their Dreamscapes, which he actually didn't use for anything bad. It was much easier for his kids to sleep through the night having good dreams instead of nightmares.

And as much as Bill would like to say it had been his plan all along, he really, truly, couldn't take the credit for it what started happening to Dipper and Mabel.

Because the twins became a little too corrupted after a while.

The problem was, no one noticed, not even their demon, until they went back home. Well, home was Gravity Falls. But this other home, with parents and school and homework and responsibilities? Was like a poison in their minds and the young kids that had started growing up wild in the Oregon woods behind the Mystery Shack, only grew up more wild and just a tad mean.

No one seemed to understand them. Except Bill of course, who was always with them. Even if no one could see him. Or hear him. And at school, kids made fun of the twins. Mabel was alright, but then, she'd always been able to stand up for herself with no problem. Though as a growing boy, Dipper got a bit more of the punishment by the ever fair high school justice system.

Unable to lash out, Dipper drew in on himself. Which made Bill annoyed and mad at his kid's tormentors, so he got revenge for them. it was with every intent to please, of course. He wanted his Pine saplings nice and happy, like they were back in Gravity Falls. Where everyone was weird and you could talk to think air and not be judged.

From there, things only got worse. Because once you begin to go downhill, you start to pick up speed.

Mabel no longer let things slide off her back. She was sickeningly sweet to you like molasses until you realized your hair was glued to your back or the answers to next week's test was hiding in plain sight in your bag for the teacher to find. She lost track of how many students she got expelled or at the very least, in detention. And she was not above using her knowledge, or Bill's powers, to get her retribution.

And Dipper? Dipper, unfortunately, was the exact opposite. In the bad way. His curiosity became overridden by fear, fear of the unknown. The ability to fight back that Stan had worked so hard to nurture over the summer dwindled into dying embers and went out all together one cold, rainy night.

Then, to everyone's horror, it came back. In the wrong ways.

Because lying in that back alley curled up, hurting and finding it hard to catch his breath, and getting rained on, something snapped in Dipper. He didn't know what it was. Maybe it was part of Cipher, still hanging around in his Mindscape. Maybe it was his own powers, brought out by the close relationship with a demon. Maybe it was nothing at all, and Dipper had imagined the whole thing.

Maybe, it was just Dipper. Whatever it was, it made his eyes go red. And it made him stand up, and told him that 'pain is hilarious' and upon that realization Dipper had focused on his attackers and well, had fought back.

Two went to the hospital with physical injuries.

One went to a psychiatric ward with mental injuries.

The last one, that's how Bill began realizing something had possibly, just a little, gone horribly wrong.

Upon closer inspection, he realized how delicious bad his little kids had become. Well, they weren't so little anymore. Bill at first, thought this was just fine.

Then things got weird.

Mabel started doing drugs.

Dipper go violent at random intervals. There was almost no way to read him.

They were shunned from high school society and often made plans in the night to hitchhike back to Gravity Falls, where they knew their Uncle would take them in and let them get away with murder.

Of course, not that they'd actually murder anyone. Ha ha.

But if they did….no, best not talk about it now.

"Are you sure you should be doing this, Pine Tree?" was a question Bill often asked as he floated after his human. Or,

"I don't think this is a good idea, Double S." was another one.

He was ignored. Mabel dropped out of school, and got a shitty job at a pizza place. Dipper stayed in school, and worked a part time job, but he was never really into his teachings in the first place, since Cipher had taught him everything he needed to know about the real world.

Then, as if things couldn't get worse, their parents told them their Uncle had died.

Dipper and Mabel ran away, into the night. And when the sun did come up, they were hidden from sight by their ever loyal demon. Traveling was hard on both of them, but they did it. Clearly the two were miserable but they grinned in an unnerving way. Cipher saw things on that desert road he'd never think his kids would encounter. He refused to let them get rides from certain strangers that offered them some quick travel.

And when Bill started saying 'no' he immediately became like everyone else in the twin's life. They yelled and shouted and rebelled, accusing the demon of trying to stop them, of never letting them get what they wanted.

If nothing changed from this moment on, Cipher shuddered to think what would happen to his Pine twins. As far as he could tell, (and he did know everything) this could end in jail, or death, or…or worse.

And when Bill was in Hell doing something or other for a brief moment, and the Devil congratulated him on a job well down twisting his latest two, pure little souls, Bill felt anger flare. He hadn't meant to do that. He'd wanted the kids to have good lives. For them to be happy. If it meant doing things that made Bill grossed out from their cuteness, niceness, so be it. But this wasn't about him or the quota he had to fill. Any day of the week he'd go and corrupt Gideon, or even Stan. (Neither would really take much of a push.) But the Twins weren't ever supposed to be a challenge. Bill hadn't meant to.

This of course, meant nothing. The other demons laughed at him. Demons are always demons, after all. Can't change that, Bill. Ashamed and angry, the Dream Demon had fled back upstairs and found it to be night time, his twins asleep on the desert floor in the shadow of an old building. As he went to wedge himself snuggly into Dipper's arms, he saw something in the dimming moonlight that made him pause and pull back.

Faded white. Splotches of red. Stains, dark and mottled on the bandages wrapped up and down Pine Tree's pale, skinny little arm.

Oh.

For the first time in his life, Bill Cipher didn't see this pain as hilarious.

Floating above their prone forms, grim and quiet, Bill did some soul searching in the dark, moonless night. He gave the twins on final, good dream, and then left. This had gone so wrong. And it was only going to get worse, that much was obvious.

So, Bill Cipher decided to do them all a favor, and hit a huge rest button on their lives.

It wasn't that hard, he knew everything. Finding a way to go back in time was easier than pretty much anything he could have done.

In the span of 5 minutes, Dipper and Mabel found themselves back in Gravity Falls. They were young, smart and kind. And, more importantly, had their whole lives ahead of them, and knew nothing of what had happened. That was part of the new deal, after all. Bill watched over them quietly, waiting for his cue.

And this time, Bill Cipher was extra careful to play the bad guy. Just as it should have been.