It was Summerween, the scariest time of summer. It's a tradition Gravity Falls had. You were in the mystery shack along with the others. Mabel was dressed as a jelly jar, Grenda as a witch, Candy as well, a piece of candy, and Dipper, who was supposed to be dressed as a peanut butter jar but is apparently feeling to "sick" to tricker treat

Dipper: "Alright so we have to collect five hundred pieces of candy before that last Jacko melon goes out."

Mabel: "Alright let's get that candy!"