Description
Some sketches of Bill possessing Grunkle Stan, or as I like to call him, Istanbill.
Been having a lot of fun speculating over what the deal is with Bill’s relationship to the Pines family. It was clear he knew about someone named “Stan Pines” from his first appearance in the show, coupled with these two posts highlighting some very interesting theories about who that person was that we saw pop his head out of the Mystery Shack in “The Time Traveler's Pig.” Fandom seems to be calling him “Stanley” so we’ll just go with that for simplicity sake.
So my stab at part of this whole mess:
Stanley may have been messing with the journal back in the day, just as Dipper is now, and while doing so might have worked with/made a deal with Bill that went sour and ended up with Stanley’s disappearance/death/whatever you wanna call it.
Stanford clearly doesn't talk about whoever this person was, and is very familiar with the danger of dealing with the supernatural. Then there’s what Bipper said near the end of “Sock Opera” that just struck me as waaay too specific for the scene, “Who would sacrifice everything they've worked for just for their dumb sibling?”
Some people speculate Stanford was the one who may have done something terrible that resulted in Stanley’s no longer being there, but I’m wondering if it isn't the other way around, which is why he was so keen on keeping Dipper in the dark about the supernatural stuff, and why he’s so secretive about whatever that machine is that he’s constructed in the basement. Which, by the way, dons the same cryptic symbol that Bill recalls upon first hearing the name “Stan Pines,” and I believe is the same symbol that Stanford has tattoo’d on his shoulder. Considering the symbol wasn't a happy memory for Bill, the machine is probably not something Bill would be approving of.
Got about a million other theories on where all this is going, but for now I’ll leave it at that.