The Summerween Trickster is a large, dark, purple monster with a yellow jack-o-lantern mask, featured in the Gravity Falls episode "Summerween".
The Summerween Trickster first appears by spying on Dipper as he discards of rejected "loser" candy from a nearby bush. At the front door of the Mystery Shack, Dipper insults the monster by repeatedly closing the door and refusing to give him the candy he desires. When Mabel willingly opens it and apologizes, the creature, disguised by a mask and coat, enters and threatens to devour Dipper, Mabel, Grenda, and Candy if they are unable to acquire 500 pieces of candy by the time of the last jack-o-melon burning out; he then crawls over the roof out of sight. Dipper, who anticipated joining Wendy at a Summerween party, has no other choice but to join the others in trick-or-treating. When Dipper refuses to wear a costume and they get only one piece of candy, however, the Trickster reappears and frightens the gang.
The kids are eventually able to obtain enough pieces of candy, but when Dipper pushes the candy supply into a nearby bush as Wendy passes by, he later discovers that the candy had fallen into a river. The Summerween Trickster then finally confronts the children, upset to discover that the candy had been lost. He then attempts to devour the children, but is run over by Soos in a pickup truck. Convinced that the monster is done for, they drive away with Soos, only for the pieces of the Trickster to reassemble into an even more hideous, malformed beast.
The gang crash into the Summerween Superstore and hide among the shelves, as the monster begins to search for them furiously. They then use costumes to disguise themselves in order to escape, but when Soos drew sound from an electronic laughing skeleton, he was devoured. The kids begin to use costume weapons to strike him repeatedly. The monster then grabs the children and reveals its true face and explains that he was made from discarded candies and planned to seek revenge from all the "loser" candy that had been ignored and discarded by the children of Gravity Falls. Soos then emerges from the monster, bursting out from its body, and begins to eat on the beast's candy innards. The monster then cries in joy after finally being viewed as delicious, mainly by Soos.