So, there was a plot to this episode, but all the action had to do with the series’ longstanding themes. The plot was to set up the three-part finale for the series, but at the same time, it was true to the characters and that makes it all the better.
See, the thing we’ve seen is that Dipper and Mabel are both not excited about being separated. Many past episodes have dealt with one or the other feeling left out and wishing things could be like they always used to. But that’s part of growing up. And the two have been growing apart in different ways. Dipper has been striving for something like adulthood, anxious to appear a man, having a crush on an older girl in the form of Wendy, and generally looking for adventures and answers to mysteries.
Mabel, on the other hand, seems to prefer being stuck as a kid. Sure, she is excited about turning 13 in a week at the end of the summer, but she also wants to stay in a constant state of the status quo in terms of her life and her relationship with her brother. The worst thing that can happen for Mabel is for Dipper to abandon her.
So, that means the two go on separate adventures. Dipper goes with Ford to find an alien superglue to seal the realty portal snowglobe while Mabel goes off to secure a place for their birthday party and hand out invitations.
Dipper’s adventure goes well eventually. He manages to rescue Ford from an alien trap…wait, aliens? Oh, of course there’s a million year old UFO under the town. Why not? Mabel’s trip is less fun. She wants to use the high school gym for her party and runs into Wendy there, and it turns out high school isn’t like some musical, but instead is a time when the classes get harder, your body betrays you, and everybody hates everybody else. And then Mabel learns she can’t even count on Grenda and Candy to come to the party. Both will be out of town.
The problem is compounded when Mabel overhears Dipper saying he’ll stay with Ford as his apprentice without Mabel. Ford has the idea that a less intelligent twin only slows you down. I wonder where he got that idea…
But Mabel gets upset and runs away with her backpack. Except she grabbed the wrong one and has the reality globe that still needs to be fixed. And then she’s approached by Blendin the time traveler. He said he can give Mabel that frozen moment if she just gets him that globe. She turns it over. He breaks it. He was possessed by Bill Cypher. And with the globe broken, a portal opens with to the nightmare realm Bill calls home.
Weirdmageddon has arrived.