exactly At the beginning of summer you were summoned by dipper to protect him and mabel. Fastfoward to now, mabel summoned someone else because you apparently spent too much time with dipper. She grew fond of them and soon so did dipper. You were barely needed now. You and the new creature got into an agruement and sadly dipper and mabel didn't take your side. So you stole his notebook and summoned bill cipher. Luckily you brought the thing ford said not to let bill get his hands on. Therefore he starts weirdmageddon.

BILL: This Party Never Stops! Time Is Dead And Meaning Has No Meaning! Existence Is Upside Down And I Reign Supreme! Welcome All! To Weirdmageddon!

The 3 watched from the mystery shack as you floated next to bill

Dipper: oh no...what have we done..