17 Dipper and Mabel vs. the Future

Mabel decides to plan her and Dipper's 13th birthday party. Meanwhile, Ford reveals to Dipper the most surprising secret yet – a giant UFO which, according to Ford, crashed millions of years ago and it's buried under the town. It was using parts of this alien technology that Ford constructed the dimensional portal under the Mystery Shack. Bill Cipher tricks Mabel into handing him the interdimensional rift, which Bill then uses to enter the physical world and open a portal from his own dimension. The end of the world begins. Guest stars: Justin Roiland as Blendin Blandin, J. K. Simmons as Stanford Pines