Hide Behind

The Hide Behind is a mysterious creature that inhabits the Gravity Falls forest.

History
Some point before the events of the series, the author of Journal 3 came across and studied the creature, recording its abilities in said book, but would have struggled because it has 'never been seen'.

In "The Hide Behind," Dipper sets out to find the elusive creature in order to prove it exists. As Dipper concludes the interview with his great-uncle, the Hide-Behind makes its rattling noise and runs out from behind the Mystery Shack into the forest. Dipper, after a number of hours chasing it, corners it behind a thin tree, which emits the rattling noise. After Dipper mistakes an owl with a maraca for it, he states that the Hide-Behind must be a legend and nothing more, as he walks off deeper into the forest. However, the Hide-Behind appears from behind the thin tree, and makes its rattling cry, as Dipper turns around, it hides behind larger trees, with Dipper unaware of its presence as it continues to stalk the young adventurer.

In "Into the Bunker" the Shape Shifter transformed into a Hide Behind after getting Journal 3, despite the journal having no clear photo of it.

Appearance
The creature is very gangly, flexible, slender, and black, with small glowing yellow eyes. It's structure is humanoid but nearly skeletal. It's limbs are incredibly long, with large hands and long fingers.

Abilities
It is flexible enough to match the trees it is hiding behind. It has the ability to change size from the height of a tree to the size of a rock.

Trivia

 * This creature is based on the Hidebehind, a creature from North American folklore.
 * This creature also bears a resemblance to Groot a character from Marvel's Guardians of the Galaxy.