warning: if you haven't seen weirdmageddon 3, the series finale of gravity falls, i advise you go to the bottom and click the link
so, a month ago, I discussed why I believed Ford will join Bill, and I was way off, that image I explained was just a hologram showing Ford what he would become if he helped Bill.
Most people speculated Stan would die by fire, and though he temporarily loses his memory, he's alive, also when Bill is trapped in Stan's mind, blue flames erupt the area in Stan's mind where they are, they could have been hinting at this.
Bill dies in the best way possible, he thinks he goes into Ford's mind, but Stan was disguised as Ford, when Bill opens the door into "Ford"'s memory, Stan is lounging on the sofa, the door then slams shut, Ford was wiping Stan's mind, as blue flames devour the room, Bill glitches out and Stan disintegrates him with a final punch.
the episode exceeded my expectations, but I had to watch it from a reaction video by MrFreakins, here's the link: