Shacktron

The "Shacktron" is a giant robot created during Weirdmageddon by the survivors of the event to fight back against Bill Cipher. Its name was coined by Soos Ramirez prior to the start of the battle it took part in.

History
After Ford created a barrier around the Mystery Shack using a unicorns' hair, it was the only place in Gravity Falls unaffected by Weirdmageddon, thus becoming a shelter and hideout for all remaining survivors. Stan mentioned that they should not attack Bill because the Shack was the only place safe from weirdness, and the only way to fight Bill is to bring the Shack to him. Realizing this, McGucket quickly drafted some blueprints to convert the Shack into a powerful machine to fight Bill and his henchmaniacs. The survivors then worked together to gather parts from all over town and assemble them together to create the Shacktron.

The survivors launched an attack on the Fearamid. While the Shacktron kept Bill and his minions occupied, Dipper, Mabel, Stan, Wendy, Soos, Pacifica, Sheriff Blubs and McGucket entered the Fearamid to free Bill's captives. Though the Shacktron managed to fend off Bill and his minions for a time, Bill ultimately discovered that only the Shack itself was immune to his power, with the rest of the Shacktron's parts being vulnerable. Bill ripped off one of the Shacktron's legs, and used it to destroy the robot.

Residents
Each of the survivors did their part in the construction and operation of the Shacktron.

Physical Appearance
The robot is composed of various objects seen throughout the series. These include:
 * The Mystery Shack
 * Parts of the Gobblewonker
 * The totem pole outside the Mystery Shack
 * Soos' Pick-up Truck
 * The Universe portal
 * Tyrannosaurus Rex
 * Foot of Gideon-bot
 * The Gravity Falls sign
 * A Lil Gideon billboard
 * A logging truck
 * Some power line poles

Trivia

 * In the game Take Back The Falls, it is referred to as the Shackbot.