No Matter What

"Thirty seconds, that's all I have?" Dipper breathed, laying his head in his hands. "That's impossible. I will never get there in time. I'm lost forever."
The day is normal, at first - for Gravity Falls. Dipper leaves the house, Mabel in tow, and they investigate new parts of the forest together, still the Mystery twins at the age of 21.
But quickly, Dipper is reminded that normality isn't the case, and never will be.
Dragged into the terrifying realm of multiverses by an old foe, Dipper must find a way back to Gravity Falls - or at least, back to Mabel. Things are frightening, tiring, and painful in these worlds, but he will not stop until he is reunited with her.

But Bill Cipher is out for blood. He does not forget easily.