A Million Days

What if Bill had invaded Grunkle Ford's mind instead of Grunkle Stan's? What if everything he had worked so hard for had been destroyed, leaving only a half-completed dream?
When Bill Cipher threatens the lives of Mabel and Dipper Pines to discover how to pop the bubble surrounding Gravity Falls that's keeping all of the weirdness in, Grunkle Ford agrees. However, when they try to outwit the dream demon, it all backfires horribly. Weirdmaggedon has been fully-realized, and it's shaking the little town to its core. Mabel and Dipper are stuck in Bill's fearamid, they must find the will to mend their broken family and survive the apocolypse, and more importantly, Bill. But when one of them crosses the line, they have to flee, leaving the other one in the fearmid to fend for themself. But what happens when the person you thought was a horrible monster might not be? What happens when the line between enemy and friend becomes so blurred you can't tell the difference anymore?
Credit where credit is due, @PerriMakenna gave me the idea for this story. You should check out her profile, she's a great person.