|It's valuable but has no other purpose.|
To obtain the Golden Pumpkin, head north after arriving at the festival. Make your way through the maze until you reach a sign that contains a question mark. Proceed through the bushes to the left of the sign, then move north into a cave. Continue east and then south until you reach the treasure chest with the Golden Pumpkin.
It also has a chance to appear inside Artifact Troves.