Ok so for months I’ve had this ask sitting in my inbox
Finally, FINALLY since its mermay I decided to do it.
I ended up liking it so much that I started thinking of lore and it all spiraled into an AU.
So I present to you:
Ford comes to gravity falls for the same reasons as he did in canon except that on top of all his other interest, he also has a degree in marine/aquatic biology. Long story short, he somehow breaks one of the seals that kept Serpas (Bill) imprisoned. He was put there like 500 years ago by the Shaman after being a destructive force of nature in the ocean for Eons. They convinces Ford to break the seal on them so that their full power can come back and they can go back to the sea.
Despite having 500 years to contemplate, Bill doesn't actually know how to break the seal, because the Shaman put a curse on it that makes them unable to see it and only a human can break it. But also it's at the bottom of the lake, which is really, unnaturally deep. So Ford needs to build a special submarine. HOWEVER. There is also a time limit because the seal can only be broken on a special event that happens every 500 years, the same night where the Shaman first sealed them. So after a few months, Ford realizes that he'll never be able to make it in time and calls Fiddleford.
And that’s how the story starts :)