stressfully
Grunkle Ford modified his portal, and instead of letting chaos into the world when it's activated, it actually sends people to different dimensions , but there is one danger : The portal changes its destination every 1 hour. If you end up stuck in one dimension, you would have to wait for an hour before you could come back to the location where you started at.
Dipper and Mabel are both curious what could be on the other side, and without Grunkle Ford's permission, they both climb into the portal and end up in ... Reverse Falls.