The Horrifying Sweaty One-Armed Monstrosity

The Horrifying Sweaty One-Armed Monstrosity is a creature who appears during the event of Weirdmageddon in Gravity Falls, voiced by Louis C.K.

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