The Shape Shifter is the main antagonist of the Gravity Falls episode "Into the Bunker". He is a creature able to take any form that it has seen and remembers.
He was voice-acted by Mark Hamill, who is famous for his performances as the Joker and Fire Lord Ozai.
The author of the journals found a mysterious egg while excavating the tunnels beneath Gravity Falls. The creature developed quickly and became extremely dangerous. The author imprisoned the Shape Shifter in a cage while they prepared a stasis tube to freeze the monster. The Shape Shifter broke free from the cage, forcing the author to flee. The author sealed the bunker, hoping that the monster would never get to the surface.
When Dipper and Wendy first meet the shape shifter, it had taken the form of an Baron Num Nums High Flyin' Beans mascot and pretended that it was the author of the Journals in order to steal Journal 3. Dipper mistakenly gives the monster his Journal, who, after looking through it, is fascinated by the many new forms it is able to take. Dipper and Wendy, realizing the danger they are in, try to take back the journal, but fail, forcing them to flee.
Dipper, Mabel and Soos blast a jet of water at the creature, accidentally hitting Wendy. The jet temporarily stuns the Shape Shifter but it attempts to trick Dipper by taking Wendy's form in one last effort to steal the journal, but Dipper attacks the Shape Shifter, knowing which is which because the Shape Shifter gave Dipper a wink, and the real Wendy zipped her lips. Dipper and Wendy push it into the stasis tube and freeze it. Before it is completely frozen, the Shape Shifter gives Dipper one last warning about prying too deeply into the mystery of the town and the author, saying it will end with his fate that is worse than he could imagine.
The Shape Shifter's default form is a pure white slimy body with four slender legs, his right arm has a three-fingered hand, and its left arm is swollen with a clawed hand. It has pink eyes and a snout with four fangs hanging on the outside of its mouth, and six smaller teeth on the inside.
- The exact origins of the Shape Shifter are unknown. It was found as an egg by the journals' author.
- A note in the surveillance room says - EXPERIMENT #210 - "THE SHAPE SHIFTER" BECAME TOO DANGEROUS! PLACED IN CRYOGENIC STASIS.
- The Shape Shifter has been shown to turn into a Gremloblin, a gnome, the Hide Behind, and five currently unknown creatures: a three-eyed toad, a creature with a fist for a head, an insectoid with an armadillo shell, a golem-like creature, and a creature that resembles a burning fire.
- The Shape Shifter takes inspiration from John Carpenter's The Thing. However, the presence of a true form, with a rather plasma-like appearance and red eyes, reflects the description in the original novel, Who Goes There?.
- According to 3, The Shape Shifter's DNA constantly changes, probably because of the forms he takes.
- The cryptogram on the Shapeshifter's entry in 3 reads: "AM I ME?, IS HE ME?"