AU where a Bill is a human (like, a spoiled rich kid anarchist) living in Gravity Falls in 1982. He still wants to destroy the world, so he summons a demon after finding a mysterious book at a local tourist trap warning of a being with incredible power whose help comes at a high price.
So enter dream demon Stanford (he’s a hexagon with a tie and twelve fingers). Bill tells him “I want to change the world” and Ford suggests he builds a portal. Except Bill is a disillusioned twenty something so Ford suggests calling a mysterious local con man and tourist trap owner (Stan) who somehow has all the parts for a portal already in his basement but no technical knowledge and Fiddleford McGucket, a computer scientist based in Palo Alto, for help.
So the portal gets built and Ford comes through and IMMEDIATELY–
–takes on a human form and goes to the store to buy some jelly beans. I mean he flies there and breaks several other laws of physics and people can definitely tell that he’s not human but he just wants jelly beans so the townsfolk leave him be.
Turns out Stan has been trying to get Ford over to his dimension for years, after being kicked out of his home at 17 and running into Ford on the road. Ford agreed to help Stan make shady deals and con people but only if Stan would allow ford to help him continue his education. So ford enlisted the help of one Fiddleford McGucket and set up a dream connection where they could all talk science (cause this is Ford: he’s not going to say he’s all knowing if he isn’t). Ford and Fiddleford became fast friends but Fiddleford and Stan never physically met each other until Bill called them up to work on the portal. (Stan kept a record of his interactions with Ford, hence the tome bill finds; the terrible price of Fords help is having to listen to his nerd talk for hours instead of just having normal dreams)
So Bill is FURIOUS that Ford isn’t destroying everything and Ford’s just “did you really think I was going to destroy your world?” cause he honestly didn’t think that was what bill wanted.
Bill vows revenge and spends the next thirty years coming up with a new universal destruction plan and attempting to defame ford and convince the townsfolk that the new demon is secretly out to get them.
Fast forward to 2012 and Stans great niece and nephew are coming to visit their weird grunkle for the summer. Ford alternates between living with Fiddleford and Stan (Fiddleford never went nuts with the memory gun, though he did build it after the Gremoblin Incident) and Dipper is ecstatic to find out that grunkle Stan is like a brother to a weird demon guy who likes weird nerdy shit (cause even though they’re not related, Stan and Ford are incredibly close– Fords human form is even modeled after Stan). Everyone bonds, but meanwhile Bill has teamed up with child psychic Gideon Gleeful and established contact with Fords previous dimension of residence– specifically, with Pyronica, Xanthar, Teeth, Keyhole, Hectorgon, Kryptos, etc. Bill makes fast friends with these interdimensional criminals and nightmares and he and Gideon make multiple attempts to steal the shack and restart the portal to let them through so they can destroy the world. Eventually, after Gideon is arrested (caught trying to steal the deed to the mystery shack) Bill runs into Blendin and beats him in Globnar. He uses his time wish to gain Fords powers, turning Ford into a human and allowing Bill to let the Henchmaniacs through.
Weirdmageddon ensues, but there’s one problem: defeating Bill this time around means sending Ford back to his home dimension. Ford is okay with that but no one else is.
Bill eventually figures out that he can’t leave Gravity Falls now, and goes after Ford, figuring that he’ll have the answer. Ford blames himself for allowing Bill to gain his powers, and refuses to give in to Bills demands. This goes about as well as you’d expect.
Eventually ford is rescued and Stan comes up with a plan to defeat Bill. He and Ford swap places and Stan pretends to take Bills deal, Fiddleford erases Stans mind and bill is defeated and all the weirdness is sucked back into the nightmare realm.
Ford is not.
Stans memories are gone. Ford attempts to bring them back with his powers, only to find those gone for good. Fiddleford explains that the memory gun worked on Bill when he was in the mindspace, but it also eliminated Fords demonic powers– so Fords a human forever now. Mabel brings Stans memories back the old fashioned way but ford can’t quite get used to being human. He’s confused and a little scared so eventually, Stan takes him aside and:
“You know, when I was a kid I didn’t have many friends. My high school principal told me to drop out cause my grades were shit, my dad kicked me out not too long after. But I remember back when I was young, I found an old sailboat lying on the beach. Totally wrecked, couldn’t sail again without rebuilding the whole thing. Wouldn’t have had anyone to sail with, either. Now, though… If you wanted, we could go on one last adventure. Buy a boat and sail around the world. You don’t have to, I just think it might help ya get used to, you know, being human.”
Ford says “My home dimension was entirely flat. Irregularity was vulgar, I was nearly killed because of my six fingers. In my youth I dreamed of a place where irregularity was celebrated or at least allowed. So I escaped through a hole in my dimension to the nightmare realm. To survive I did… Some unspeakable things for the henchmaniacs to obtain power, things I regret to this day. The last straw though, was when they wanted me to destroy my home dimension. I’d spent so long revelling in my differences, but when I went back to my home…. I couldn’t do it, I couldn’t destroy an entire world.I’d forgotten something. Differences make us who we are, but it’s important to find someone to share common ground with.”
“… Okay that was beautiful but what did it have to do with anything?”
“I’d like to go sailing with you, but I don’t want to leave behind another home. I fit in here, people know me here.”
“well no one’s saying well never come back”
And so they go on periodic boat trips and Soos officially runs the shack and Dipper and Mabel visit all the time and everyone is happy except for Bill who is dead.