It’s about Darlene, an employee of the tourist trap known as Mystery Mountain, who appears in the Season 2 episode “Roadside Ride”. She is voiced by none other than Chelsea Peretti, best known for her role as Gina Linetti on Brooklyn Nine-Nine. She is a sarcastic and selfish civilian administrator of the site, whose narcissism is so extreme that she was once called a psychological anomaly by a group of professors.
In “Roadside Attraction”, Darlene appears as Uncle Stan’s short-lived love interest (voiced by Alex Hirsch), although this ends abruptly when it is revealed that she is in fact a half-man/half-spider hybrid known as the “Arachnimorph”. Darlene confesses to using her human form to lure men into her lair and eat them, and she ends up trapping Stan in a large web before being rescued by Dipper and Mabel.
While fans of “Brooklyn Nine-Nine” may not immediately recognize Peretti’s voice (especially since she delivers her lines in Gina’s non-bored, sardonic tone), once you recognize her, it’s hard to hear anyone else.