The Horrifying Sweaty One-Armed Monstrosity

 is a creature who appears during the events of Weirdmageddon.

History
In "Weirdmageddon Part 1," The Horrifying Sweaty One-Armed Monstrosity encounters Dipper as he attempts to break in to the Gravity Falls Mall in search of his friends. He demands that Dipper climbs into his mouth, which Dipper ignores in terror, much to the monstrosity's frustration. He later appears when Wendy and Dipper are trying to avoid Gideon and his henchmen, where he eats one of the Discount Auto Mart Warriors. He also appears during the episode's end credits, who desperately tried to convince anyone to climb in his mouth. But sadly failed and slowly inch away to go call his mother.

Appearance
He consists of a gigantic man's head, with a round nose, a five o'-clock shadow, thick red eyebrows, and a red hair. Attached to the top of his head is a muscular arm which he uses to drag himself around.

Quotes
"Anybody wanna get in my mouth? I'm a big mo—hungry monster—I'm a big hungry monster here! I would really appreciate it, if someone—you, ma'am, you ma'am, how would you like to get in my—"

- The Horrifying Sweaty One-Armed Monstrosity during the end credits

Trivia

 * Louis C.K., the creature's voice actor, improvised most of his role during the end credit scene of "Weirdmageddon Part 1" where he says, "I gotta call my mother." In fact, there is nearly 30 minutes of him improvising different ways the monstrosity could beg someone to get into his mouth.