I'm to lazy to keep doing this so here's a lijst of all my theories and some evidence.
-Dipper's real name is Issac. In Fight Fighters, Dipper enters the initials D.I.P, which could stand for "Dipper" Issac Pines.
-Gideon is a vampire. In Weirdmegenton 1, Gideon says, "She was always meant to be mine". I guess this means that he's a vampire cause vampires are immortal. There is also other stuff that supports this and u can look it up on YouTube, but I can't help u there.
-Bill is still in Dipper's mind. In Northwest Manor Mystery, Dipper reacts to Mcguckets warning with the line, "Let's have some fun for once". He doesn't care and he walks of with his fits on his hips a thing only Bill did when he was possessing Dipper. Also in Stan's Not What He Seems, there is that one scene where Dipper's eyes look like how they did in sok Opera when Bill was possessing Dipper.
Um...I can't think of anything else. So, I'll just get back to reading and writing fanfics.

Bill has found Hazel, Mabel, and Dipper and has made a little family reunion but with who? Mabel and Dipper of Hazel? Well, the danger is growing as Bill makes a deal with one of them. But, will they accept it? Hazel has a secret and the others know it. Will it make her a threat of will it help the Pine Twins? These vragen and meer will be answered in Gravity Falls: The Years Afterward Part :2.
It will get very crazy because I read a bunch of fanfictions about Bill and the Pine Twins so be prepared!