Gravity Falls AU: Mason and May

Other title ideas/ working titles: M&M, Skele-Twins, Chaos Falls
The Mason and May thing is largely to differentiate them from Canon!Dipper and Mabel but it's also their preferred names in story for the most part.
I spend/spent a lot of time thinking about what I would do in various scenarios and character situations in Gravity Falls (usually Dipper or Mabel, often the Author, and oddly enough, Wendy). I also tended to ask one of my best friends, who introduced me to the show, what he would do. I eventually realized that some of those decisions would have really interesting results, and the two of us had personalities that work well with the rest of the Gravity Falls gang. So, how in detail would the story go if Mabel had my personality and Dipper had my close friend's personality?
While yes, this is technically a self insert fic, I'm going to do all in my power to stay away from the Mary Sue pit. Watching and learning from reviews of things is one of my favorite things to do, so I've learned a lot about writing a good character and stories in general, and "Mason" will always be there to peer review. I know about horrors like My Immortal and writing one of those would be one of the worst things I could ever do.
Teasers for the actual story:
*The twins spent the last couple years of their lives at a middle school filled with generally terrible kids (nothing on Gideon's level) and no one there to get along with but each other. This has had a major effect on both of them: their faith in humanity and willingness to trust others, to start. But while May struggles to remain optimistic, Mason is one of the most pessimistic people you've ever seen. He never really has a chance to act on what this all...ahem, inspired him to do, until he meets Bill, and realizes he has a golden opportunity on his hands.
Description is continued in first "chapter" thing.