Before the twins' visit
Granny Sweetkin is one of Stan's tourist trap competitors who prank the Mystery Shack every year. The year before Dipper and Mabel came to stay with Stan, they duct taped Soos to the ceiling, leaving him there for 78 hours.
In "Roadside Attraction," the first stop of Stan's trip of revenge is Granny Sweetkin's tourist trap. While the gang is there, they tie one end of the yarnball to their RV's bumper, so that they unravel the ball as they leave. Granny Sweetkin turns out to be inside the yarnball, and when it unravels, she gets angry, runs after the RV and throws a giant knitting needle at it like a javelin, which impales itself into the back of the vehicle. She later vandalizes the Mystery Shack along with the other tourist trap owners.
Granny Sweetkin may look like a nice old lady, but she can get very aggresive when provoked, swearing in an eldery manner, using elements from her surroundings as weapons and vandalizing others' property in vengeance.
She is a very old lady. Her hair is gray and worn in a bun. Granny Sweetkin has a wrinkly light skin and a nose darker than the rest of her skin and wears a light blue dress and brown shoes.