The Shape Shifter, (a.k.a. Experiment #210) is a creature able to take any form that it has seen.
In "A Tale of Two Stans" Stanford Pines found a mysterious egg in the forest that later hatched into what he would come to call the Shape Shifter. The creature developed quickly and became extremely dangerous, so Ford imprisoned it. When he prepared a stasis tube to freeze it, the Shape Shifter broke free. Ford managed to escape, sealing the Shape Shifter in the bunker, hoping that the monster would never be able to get to the surface.
When Dipper and Wendy first meet the Shape Shifter, it is in the form of a bean can mascot, pretending to be the author of the journals in order to steal Journal #3 from Dipper, who mistakenly gives the monster from his Journal, who, after looking through it, is fascinated by the many new forms it is able to take. After realizing the danger they are in, Dipper tries to take back the journal. After Wendy is able to stun the Shape Shifter so that it drops it, the two flee.
After running into Mabel and Soos, they formulate a plan to get rid of the Shape Shifter. 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. The Shape Shifter attacks Wendy, and Dipper becomes confused by who is who, asking the real Wendy to give him a sign. When the real Wendy zips her lips, Dipper hits the Shape Shifter with Wendy's axe, and the two of them push the monster into the stasis tube to freeze it. Before becoming 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 a fate that is worse than he could imagine. The last form it takes is Dipper screaming, saying it is "the last form he (Dipper) will ever take" (an event that later happens in "Northwest Mansion Mystery.")
It also appears in Ford's flashback in "A Tale of Two Stans," by hatching out of an egg that was dug out by him in the forest. It then takes the form of a mug that was placed by its side.
The Shape Shifter is a cunning, quick-thinking, and manipulative creature. Without even knowing Dipper, Wendy, or their quest for the author, it was able to effectively set up an elaborate ruse to win their trust and gain the journal.
Its abilities enable it to change not only its appearance, but also its entire form, including its voice. Thus, it can be as small as a Gnome or as tall as a Hide Behind or as amorphous as fire. Its desire for the research journals in order to assume different forms seemingly indicates that it can't change unless it's "scanned" a form or seen a picture of it. It can also "mix" forms to create new monsters, or become two things at once.
- 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 man based on the mascot of a brand of canned beans, a Gremloblin, a gnome, the Hide Behind, Mabel, Dipper, a Dipper-Mabel composite monster, Wendy and six currently unknown creatures: a spider creature (shadow only), 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 some burning fire in "Into the Bunker." It can also turn into a cup similar to the one beside it when it was just hatched out from an egg in Ford's flashback in "A Tale of Two Stans."
- The Shape Shifter transformed into the Hide Behind, despite the fact that the journal has no clear photo of it.
- Its true form was also inspired by Clayface from the animated Batman series and is based off of a Vietnamese eggroll that character designer, Robertryan Cory, once ate.
- According to 3, The Shape Shifter's DNA constantly changes, probably because of the forms it takes.
- The cryptogram on the Shape Shifter's entry in 3 reads: "AM I ME?, IS HE ME?"
- It appeared on the Gravity Falls Season 2 poster.
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