Jack-o'-melons are used as decorations during Summerween. They are similar to jack-o'-lanterns, except they are made from watermelons instead of pumpkins. In the summer, the Gravity Falls residents light up Jack-o'-melons for the holiday of Summerween. They are made notable by the Summerween Trickster, who was going to eat Dipper, Mabel, Candy, Grenda, and Soos if they did not get 500 pieces of candy before all the candles in all the melons were extinguished.
Traditionally, jack-o'-lanterns are made out of pumpkins. But for Summerween, jack-o'-melons are made with watermelons, hence their name. Jack-o'-melons are seen throughout the town of Gravity Falls, where residential homes are decorated with them in spirit of the holiday.
Jack-o'-melons resemble jack-o'-lanterns, except they are made from watermelons instead of pumpkins. Similarly, they both have faces carved into them, and a lit candle placed inside them.
- 112. "Summerween"