[ I love the idea of there being aftereffects to Bill possessing Dipper, so the Permadipper AU is alllllll kinds of up my alley. It’s so interesting to think about how Dipper would cope as his time in the mindscape started to have an effect on his appearance. I feel like it would happen in chunks or stages, and concentrating on looking normal would help at first… but eventually he would wind up going full triangle and completely freaking out.
With Mabel’s help, I imagine that he’d eventually get a handle on things and adjust, mostly by constantly reminding himself that it’s all just temporary until he gets his body back. So he would do things like walking instead of floating whenever possible, even though it’s inconvenient, because it’s a way to (quite literally) keep himself grounded.
And after a little while, things might even almost manageable. But dream demons can’t sleep, and Dipper doesn’t want to be like Bill and run around inside of people’s heads unless he absolutely has to. So after all the research he can do starts to run out, he spends a lot of time alone with his thoughts at night. Wondering where things can possibly go from here, rethinking over and over whether there’s anything he hasn’t tried.
Eventually, all that frustration and helplessness wearing him down starts to turn into something else. Little moments when he catches his mind wandering, having random thoughts that don’t even seem like they’re his anymore. Mood swings where he’ll get more enraged than he thought was possible, or finding things funny that really shouldn’t be. They never last for long, but they horrify him even more than losing his human form did once he realizes what…or rather, who, he’s starting to act like.]