He had gotten into a really bad argument with his twin brother Stanley and he accidentally hit the switch of the portal to another dimension. Things start floating around and he panicked as he realized he was about to get sucked in. He quickly took off the baby strap on his back and thew his daughter at his brother Stanley and then threw the journal he was holding at him too. he then got sucked in.

20 years later

Finally he was free from the dimension. but he was pissed at is brother for fixing the portal, it could have ripped the universe apart, luckily at didn’t. he didn’t realize there was children there. Mabel and dipper, and two other adults, Sues and…his daughter.