Ep 18. Weirdmageddon Part 1

When the town of Gravity Falls is invaded by Bill Cipher, the infamous triangular dream demon, in the first part of the epic three-part finale of season two, Weirdmageddon Part 1, Dipper, Mabel, and the rest of the town's inhabitants must band together to fight against the chaos that ensues.

As Bill Cipher unleashes his power upon the town, the Pines siblings quickly discover that he has turned the world into a twisted, apocalyptic version of Gravity Falls, and that they are now trapped in it. Along with their friends, including Grunkle Stan, Wendy, and Soos, they must navigate through this new reality, facing off against Bill's minions and trying to find a way to defeat him.

Throughout the episode, the Pines siblings and their friends encounter many bizarre and frightening creatures, which include a giant spider, a pack of gnomes, and a group of maniacal toy robots. They must use their wits and their skills to outsmart these creatures and stay alive in the new world created by the demon.

Meanwhile, back in the "real" world, their family members and other characters who were not present during the invasion must figure out how to get the Pines siblings and their friends back and defeat Bill Cipher. They enlist the help of Ford, the long-lost twin brother of Grunkle Stan, who has been studying Bill Cipher for years and has developed a device that he believes could be the key to defeating the demon.

As the episode comes to a close, the situation looks bleak for our heroes. Bill Cipher seems to have all the power in this new reality, and it is unclear whether they will be able to find a way to defeat him and save Gravity Falls before it's too late.

Overall, the episode is a thrilling and suspenseful ride, full of twists and turns that keep viewers on the edge of their seats. It sets up the final two episodes of the season, which promise to be even more epic and action-packed, as our heroes face their toughest challenge yet in their fight against the evil Bill Cipher.