Author: Hello there! Here is simply a collection of all the Gravity Falls oneshots I've written so far, in one neat convenient little collection for you to read! Please feel free to leave your own prompts for this series in a review if you'd like.This is the very first thing I'd ever written for GF.

Prompt: Does Bill's fondness for the twins give them any kind of unnatural life span (meaning they have to watch others around them getting old) or does Bill have to deal with them aging (at what must seem like a super fast rate to him)?

And Demons Behaved

If you had told Bill Cipher half of what was going to happen when he first started getting attached to the Pine Twins, he would have laughed so hard his hat fell off. And then he had have given you nightmares with nothing but giant spiders and taking tests in your underwear for the next six years of your pathetic human life. He was that kind of demon you see, and he was a very good one. He did his job, did it well. And above all, enjoyed making deals and using humans are cute little puppets.

He'd just never encountered these humans before.

Well, maybe he had, long ago. When you were Bill Cipher and you knew everything, it was hard to remember what had and hadn't happened yet.

At first, it wasn't a problem. Maybe a bit of an annoyance, but hardly a thing that required his attention.

Pine Tree was nosy. Shooting Star was obnoxious. And glittery.

He had no reason to think otherwise.

Until suddenly he did.

Bill's mind was in complete chaos after he realized how attached he was to these little runts. Normally, he liked chaos. Not this kind. This wasn't right. This wasn't how things were supposed to go (Except, yes they were. Exactly.) When they were happy, it was contagious and he found himself cheerful. They enjoyed his stories and he found himself, to his disgust, tagging after Pine Tree like a puppy. Mabel knitted him a sweater. They pranked Grunkle Stan together, and unraveled the many mysteries behind the Journals. When one had a nightmare and called for him, he came, without thinking. Anyone who made the mistake of harming his twins was met with Cipher's bottomless wrath and all the protectiveness of a mother bear, backed by demonic powers. No amount of Bill's fighting or feigned ignorance had stopped him from getting far too attached to the Pines siblings. He knew it was going to happen, and yet hadn't really done all he could to stop it, had he?

It felt like it happened over night, to be honest.

Pine Tree was curious. Bright, but in a different way than his sister. Clever and surprisingly fierce when his protectiveness over his family was provoked. Dipper's mind was dangerous. Bill liked that.

Shooting Star was loud, but friendly. Hopeful and sunny and adamant in not throwing the bedazzled towel in too soon, if she could help it. Bill admired that.

Mabel bedazzled Bill's cane once. He got another one right after, but instead of destroying the glittery cane kept it to use when he felt like it. He didn't say thank you—because demon's don't say thank you.

But he didn't get rid of it.

Against his better judgment and every fiber of his being telling him he knew better, Bill completely and utterly failed Demon 101. Which was of course, never ever get close to your targets. They hadn't even been targets until he decided so. (Or had something decided for him? He couldn't remember.)

He does remember what happened after they became friends.

Time became a bitch, and it sped up.

Horrifically fast, if you ask Bill. One blink, and his kids were in their 20's. Another blink, and 40's. 50's. 60's. 80's.

Bill Cipher was mortified when he realized his children had grown up around him like pine trees in the forest. Where had his bite-sized human children run off too this time? Why had those summers gone so fast—why was Mabel sporting silver hair and Dipper needed glasses? It was only a second ago that they…

Bill wanted them back. They had no right to leave him. He hadn't given them his permission. They'd broken the rules of their unspoken deal. And that was, 'You are mine. You will always be mine. I will take care of you. And you will be with me.'

Deal.

At first, Dipper and Mabel had laughed at him softly, teased him a bit over his sudden realization toward their old age. But they sobered up when they realized he was completely serious. And a bit heartbroken, if they were reading between the lines right. (After a lifetime knowing a demon, they were both keen spotters of lies and fibs and knew what they heard in the demon's hurt voice was something deeper, thicker and painful.)

Bill had come to terms with their age, after much coddling and coaxing from his twins. Out of the blue, Mabel was often taking the hand of a gentleman with yellow hair and an even yellower suit. He would help her up and let her use his arm to shuffle where ever she needed to be. She smiled at him, and he smiled back, though it was much more strained. Bill and Dipper started a game of Chess that went on for hours. They kept track of the wins and losses. At his best, Dipper tied with a demon so much that they'd given up the sport altogether. Now, they were back at it, and the odds were uneven again. Bill won chess more and more often, but at the same time felt like he was losing something. He didn't figure it out until it was too late.

For a moment, for one beat of his black soul things were almost better again, like they'd used to be.

Then the twins…they got…worse.

Did you know? Human minds deteriorate. Bodies, too.

At first, Bill never noticed humans doing it. When he did, he was highly amused at such a weakness. Then the novelty wore off and he forgot about this illness altogether. This was sometime around 1705, when Bill Cipher the Dream Demon finally discovered the dying process. So he'd pretty much put it from his mind by the time his moment with the twins rolled around.

Now, as Mabel began misplacing things and Dipper's eyesight got worse, Bill hated this weakening business. He loathed it. He got angry, and shouted and yelled and was careful to never have a tantrum near his twins. He feared what they'd say or think if they knew their childhood protector was behaving in such a way.

Their hands shook. They forgot things, places, people, names. Stumbled. Had bruises on their tired, fading flesh. Squinted to see and had the tv on loud, like Stan used to.

Bill couldn't help but watch on, feeling more and more useless with each passing day.

Mabel could no longer stand.

Dipper forgot how to play chess.

Then, one day, they both became unable to see their demon altogether.

Demons of course, and the magical-like, didn't exist.

Bill didn't know the demonic equivalent to a broken heart, but he knew he was feeling it then.

Thankfully, Dipper and Mabel had been of sound mind before this. And they told Bill things. Asked him. Suggested. Promised they loved him and their children and grandchildren would love him too, if only he behaved and gave them a chance. Didn't scare them too much. Tucked them in, gave them sweet dreams. All the things he used to do for the twins so long ago, Bill was asked to at least continue with the Pine's siblings family.

He'd done what they'd asked of course. Been a good little demon and outright obeyed them, partly out of fear Mabel would do what she'd threatened if he didn't. (Which was come back as a squirrel and chew up his hat, apparently.) And partly because he really had loved them so much that by the end of it he loved their kids, too. Humans had weird little offspring that kept going, and for the most part, history likes to repeat itself.

Bill had done what he could manage without getting too depressed about it all. Granted, it hadn't been much looking back. What was a couple hundred years in his life? It didn't amount to much, in term of round figures.

But then fuck, why did it hurt so much when they left him? What right did they have, to go away where he couldn't follow? How dare they leave him! That was problem with befriending good little souls. He was mad at them, at first. When Mabel passed away first, Dipper had followed not 5 minutes later. He was across the state; the siblings were still close but had their own lives. And what lives they'd had, surrounded by offspring, by little grandchildren who adored them and children who made sure they were comfortable until they passed in their sleep. Their lives had, for the most part, been remarkably good. Bill shouldn't be looking Fate in the eye and challenging her too much.

He remembered their deaths with startlingly clarity. And Bill remembered their last two sleeps. He had given it to them, as a goodbye gift. For a few moments, until their bodies gave out, Mabel and Dipper dreamed of being children. They dreamed of the soft glow of the summers living in the attic, and the creatures and monsters and demons they encountered, fought, and befriended. And for the shortest of moments they were back in Gravity Falls, and the year was 2013, and the Mystery Shack still stood and it said 'Mystery Hack' really, and Grunkle Stan had the tv too loud. And Soos was fixing something, and the world was sweet and honey golden and the carpet was worn but familiar. And the Journal was being poured over and Dipper was mumbling to himself about it, and Mable was playing with Waddles on the floor and…

And it ended. Just like that. They ended.

Mabel slipped from Bill's fingers. Dipper followed. Neither of them seemed angry or scared to go, and sometimes Bill wished they had shown some negative emotion. If they were scared, he could have swooped in and saved them like he'd always done. If they didn't want to go, maybe he could have made a deal with Death. Maybe he could have done the impossible.

Those two certainly had done the impossible enough.

Up here, high on top of this hill among gravestones Bill Cipher decided he'd done the best he could, given the circumstances. It's not every day a demon falls in love with children. Certainly not every day said demon willingly stays with them, cultivating some twisted form of what Bill could only pin down as affection. He'd tried to make them happy. It had taken some work, but by the time they were elderly and dying, he'd learnt enough to feel desolate remorsefulness at not being able to hear Dipper's voice or see Mabel's smile. He'd tried his best though. And in the end, that's all that ever mattered to those two.

So he stays up here, on his little hill with Dipper and Mabel on either side. Mabel can see the pond below and Dipper's got a nice view of the stars. He was glad, if they had to end up dead and gone somewhere, it was a nice cemetery like this. Stanford is somewhere, maybe to his right. Bill isn't sure. He isn't going to move from his spot to check. It's a family plot, but Bill was only really ever interested in his kids anyway.

The gorgeous tangerine sunset that spread over the little valley of graves was just coming back to him as something beautiful, instead of the reminder of an end.

After they had died, Bill Cipher went back to being a demon.

After, Bill Cipher had said 'never again' and moved on.

But no one around him dreamed for a while.