Shape Shifter

The Shape Shifter (aka Experiment #210) is an intelligent creature found in the bunker of the Author, and appears in the Gravity Falls episode "Into the Bunker". Like its name suggests, it can take the shape of anything that it sees as well as becoming surreal combinations of forms. Dipper, Mabel, Soos and Wendy come across it while exploring the bunker, where it attempts to escape into the outside world. It is voiced by Mark Hamill.

Background
The Shape Shifter was kept by the Author years before present day when it was found as an egg. The creature developed quickly and became extremely dangerous, so the author imprisoned it in a cage while they prepared a stasis tube to freeze the monster. The Shape Shifter broke free of the cage, forcing the author to flee. The author sealed the bunker so that the monster could never escape. When Dipper and Wendy arrive, it takes the form of a bean can's mascot and pretends that it was the author in order to steal the journal. Dipper mistakenly gives the monster the journal, who, after looking through it, gains many new forms. Dipper and Wendy are forced to flee once they discover what the monster is.

Dipper, Mabel and Soos try to defeat the Shape Shifter by blasting water at the creature, accidentally hitting Wendy. Although stunned, the creature attempts to trick Dipper by taking Wendy's form to steal the journal. However, Dipper is able to figure out which Wendy was the false one and helps the real 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 and takes the shape of Dipper screaming as its final form to horrify him.

Physical Appearance
The Shape Shifter's default form is a pure white slimy body with four slender legs. Its 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.

Personality
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.

Trivia

 * 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?".