Dipper, Mabel, Soos, and Grunkle Stan drive to the Summerween Superstore to prepare for Summerween. Stan explains that the locals wanted to celebrate Halloween twice a year, so they created Summerween, a Halloween in the middle of Summer. Soos finds punny cackling skulls in the store and he keeps turning them on, much to his amusement. Mabel and Dipper are trashing the store in a wheelbarrow, while Grunkle Stan gets some material for scaring trick-or-treaters. The cashier calls security due to the disturbance they're making, so Grunkle Stan throws a smoke bomb at the cashier and runs away with the gang, paying for the things with "Stan Bucks," Stan's poorly drawn counterfeit money.
Dipper and Mabel are planning out Summerween when Soos tells Dipper and Mabel about the Summerween Trickster. If the children do not enjoy their candy, the Summerween Trickster eats them alive. However, Dipper begins throwing out candy that he deems as trashy "loser candy" that Stan had bought to hand out, unaware that the Summerween Trickster is watching him from afar.
The doorbell rings and Dipper goes to get it. Dipper is surprised to find Wendy and Robbie at the door. When Robbie asks Dipper if he is going trick or treating, Wendy tells him that Dipper isn't because trick or treating is for kids. Dipper reluctantly agrees with her. Wendy invites Dipper to Tambry's Summerween party, and Dipper says he will go. However, Mabel has invited Grenda and Candy to go trick or treating. Dipper fakes being sick so he can go to Tambry's party. However, the doorbell rings again, and this time it's the Summerween Trickster. Dipper mistakes him for a normal trick-or-treater, says he is too old for trick-or-treating, and slams the door on him. The Trickster knocks on the door again, but Dipper slams it in his face, getting the Trickster angry. Mabel scolds Dipper and opens the door again. The Summerween Trickster now breaks into the Mystery Shack and tells him, Mabel, Grenda and Candy that if they don't deliver 500 pieces of candy to him by the time all the Jack O' Melons in town go out, he'll eat them, proving that he will keep his promise by eating a random trick-or-treater named Gorney who arrives at the shack.
They head over to Lazy Susan's house to trick-or-treat. Because Dipper refused to get dressed up, they only get one piece of candy each, and he receives none. So, Mabel decides to dress Dipper up and act cute whenever they go to houses, which greatly increases their candy yield. Eventually they end up with 499 candy pieces, and Mabel decides to go get the last piece with everyone but Dipper while Soos goes and gets his truck so they can deliver the candy. Unfortunately, Wendy and Robbie arrive in their van and Dipper takes off his Summerween costume and pushes the supply of candy behind a bush.
When Dipper says he will be there soon, Wendy and Robbie take off in his van and Mabel discovers why he faked being sick earlier. It doesn't get any better, the candy has fallen off a cliff behind the bush and into a river because Dipper had not been paying attention, and everyone begins blowing out the candles in their Jack O' Melons. Dipper, Mabel, Grenda and Candy manage to stop Old Man McGucket from blowing out his Jack O' Melon, but when they breathe a sigh of relief, the Jack O' Melon goes out. The Summerween Trickster then arrives.
Meanwhile, Grunkle Stan is having a difficult time trying to scare two kids. He even has Waddles burst out of his chest in an attempt to scare them, but the kids are not scared due to watching horror movies ever since they were two years old. The kids scare Grunkle Stan with a 'screamer video', and Stan runs back in the Mystery Shack in disgrace.
Soon, the Summerween Trickster tries to eat Dipper and Mabel, but out of nowhere, Soos drives his truck straight through the monster, smashing him to pieces. The kids get into the truck, but Mabel gives Dipper the cold shoulder for not wanting to trick-or-treat with her.
Unfortunately, the Summerween Trickster comes back to life as his pieces re-assemble, and he pursues the truck. Dipper, Mabel, Grenda, Candy, and Soos hide in the Summerween store, and Mabel reveals she was upset with Dipper because she was worried this will be the last time they'll trick or treat.
They are almost in the clear when Soos turns on a cackling skull that he was playing with earlier and the Summerween Trickster finds them. The Summerween Trickster reveals to be an amalgamation of pieces of "loser candy" no one wanted and tossed in the dump. It eats Soos and then tries to eat Dipper and Mabel. However, Soos eats the monster from the inside out, and the Trickster collapses. The Summerween Trickster then confesses that all he wanted was someone to enjoy his candy, and he starts crying tears of candy corn as Soos happily eats him.
Grunkle Stan finally manages to scare the two kids after they accidentally see him half-naked in his bathroom, and the kids drop their huge sacks of candy while running away. Dipper, Mabel, Soos, Grenda, and Candy finally get back to the Mystery Shack and find Wendy back early from the party. Dipper confesses to Wendy that he was trick or treating, but she replies that the party was lame because Robbie ate a lollipop stick-first and had to go home early. In the end, everyone watches TV eating their candy. Grunkle Stan explains that Summerween isn't about candy or scaring, but a night to celebrate pure evil. After some maniacal laughter, Soos confesses, "I ate a man alive tonight" and everyone glances strangely at him.
"Summerween" made its home video debut on the Gravity Falls: Even Stranger DVD, released by Walt Disney Studios Home Entertainment on August 26, 2014. It was made available again, along with the rest of the series, on the Gravity Falls: The Complete Series DVD and Blu-ray sets, released by Shout! Factory (under license from Disney) on July 24, 2018.
- Viewership: This episode was viewed by 3.478 million people on its premiere night.
- The Summerween Trickster can be seen among the pictures in the theme song, albeit with an apparent orange skin color.
- This episode takes place on Friday June 22, 2012 as seen on Stan's calendar.
- Candy's photo of the Trickster has the equivalent of the English term, "awesome" in Korean on it, according to Niki Yang.
- Despite the agreement Robbie and Dipper made to secretly hate each other in "Fight Fighters," Robbie still outwardly insults Dipper near the start of the episode.
- Stan's car, when he gets to the Summerween Store, says El Diablo on the side, which means "The Devil".
- In the part when the kids battle the Summerween Trickster, Dipper's shield has a pyramid with an eye on it.
- After Soos bursts out of the Summerween Trickster the piece of the Trickster he is eating is in the shape of a heart.
- During the end credits, the cryptogram says "YILFTSG GL BLF YB SLNVDLIP: GSV XZMWB." Once translated it reads: "BROUGHT TO YOU BY HOMEWORK: THE CANDY." Homework: the Candy is one of the brands in the Mystery Shack's bowl of "loser candy."
- The "Explosion Muffin" that Robbie spray painted on the water tower appears once again.
- The 90s teenagers that caused Pa and Ma's death are shown again as contributing factors to the creation of the Summerween Trickster.
- Robbie and Wendy are still dating after Robbie is seen asking her out in "The Time Traveler's Pig."
- In the scene where the boy pair shows Grunkle Stan a video of a kitten about to sleep but unexpectedly changes into a demon screaming, it resembles Regan's demon face from The Exorcist, which got infamous from Scary Maze Game and unusual pranks from YouTube videos and many other tricks.
- When Waddles jumps out of Grunkle Stan's stomach, it is a reference to the Ridley Scott film Alien, in which the aliens impregnate the humans by laying their eggs in the human's mouths. When the eggs hatch, they pop out of the human's chest, killing them.
- The Summerween Trickster's first form and the overall events are a reference to the movie Trick 'r Treat where people are killed by a little monster if they do not respect Halloween's traditions.
- The Summerween Trickster is a reference to Spirited Away's No Face.
- The Summerween Trickster may also be a reference to Slenderman, a monster created over the internet that even has his own video game called Slender.
- At the end of the episode, the pictures of Waddles with text are a reference to the I Can Haz Cheezburger meme pictures.
- The sword and shield that Dipper fights the Summerween Trickster with is a reference to the Master Sword and Hyrulian Shield that Link uses in The Legend of Zelda. The shield has the Eye of Providence on it as well.
- Dipper sliding between the Summerween Tricksters legs and attacking his back is a reference to the final boss in The Legend of Zelda: Ocarina of Time, where Link must roll between Ganondorf's legs and attack his back to defeat him.
- At the credits, the phrase "I hate Mondays" is a reference to the famous newspaper comic strip Garfield.
- The Summerween Trickster being made of candy is an allusion to the The Nightmare Before Christmas villain Oogie Boogie, who was made of bugs.
- Waddles' costume is similar to Animal Farm where, at the very end, the pigs start wearing suits.
- Grunkle Stan calling himself the "Master of Fright," along with the little hand motion, is another reference to The Nightmare Before Christmas in the song "Jack's Lament"
- A candy called Blorch makes several cameos. This sweet shares the same name as a planet in Nickelodeon's Invader Zim. The planet is home to slaughtering rat people.
- The candy Mr. Adequate-bar is a reference to Mr. Goodbar.
- When Stan pulls up to the Summerween Superstore, he parks in front of a handicap parking sign. However, the sign is facing away from the parking spot instead of toward it.
- When Mabel opens the door for the Summerween Trickster, Dipper was standing near. However the door never hit Dipper, nor was he there after, but appears later on.
- In Mabel and Dipper's music number for Halloween at the biker's house, the treat bag disappears. When he gives them the candy, after it ended, it reappears in their hands.
- During a few frames, the strawberry on Mabel's costume leaned in a different direction.
- When Soos' truck was recklessly driving through town, it had a blanket draped on the back end of the car. After the car crashed into the store, it disappears.
- When Soos hits the Summerween Trickster with his truck, Gorney can not be seen. But in the store when Soos is eating out of the Summerween Trickster, Gorney comes out.
- In the Summerween Superstore, the skulls in the bowls are in different areas when they first get there and when Soos crashes his truck into the store.
- In one of the opening frames, the lettering on the water tower that usually reads "Gravity Falls" is gone. Also, the walkway where Mabel took Grunkle Stan in the previous episode(s) isn't there.
- When Candy says she took a picture of the Summerween Trickster, she never pulls her phone out when she first met him.
- Waddles has a light brown/tan spot on his left eye rather than his right eye.
- When you first see children Trick-or-Treating, Waddles is with a random child, Candy and Grenda walking by themselves, and Gorney appearing on the top-left even when he was eaten.
- The Summerween Trickster's eyes are peppermints, but after when Soos was eating him and he was screaming in pain and he fell on the ground his eyes are just yellow dots.
- When Dipper is shocked to see Wendy with Robbie, he drops some candy from the bowl on the ground. When Wendy comes in the Mystery Shack with Robbie to get her jacket, no candy is seen on the floor.
- In the promo for this episode, the Summerween Trickster was a brighter shade of purple than in the actual episode.
- When the Summerween Trickster is talking about "every discarded bar of chocolate with that white, powdery stuff" he's explaining it with both hands, even though he only had one free hand.
- The Summerween Trickster said Dipper, Mabel, Candy, and Grenda had until the last jack-o-melon goes out to get 500 pieces of candy. Yet when the Summerween Trickster came to get his candy, Stan's jack-o-melon was still lit.
- Twice in the episode, the Summerween Trickster shows its mouth: when he eats Gorney and when he is searching for Dipper, Mabel, Candy, Grenda, and Soos. However, when the Trickster reveals his full face, his mouth was under his mask.
- When the Summerween Trickster first goes into the store for the kids, he tears the door off of Soos's car. When it shows the kids running around behind the Trickster, the car still has the door.
- Dipper's watch disappears when he first opens the door to the Summerween Trickster then re-appears when Dipper closes the door.
- Waddles's light brown/tan spot has been replaced with pink spots instead of light brown/tan spots, when he's eating the candy in a bowl.
- Waddles' fake suit is stiff when he first appears; but later it folds when he goes to eat candy.
|Kristen Schaal||Mabel Pines|
|Jason Ritter||Dipper Pines|
|Alex Hirsch|| Grunkle Stan|
Old Man McGucket
|Jeff Bennett||Summerween Trickster|
|Linda Cardellini||Wendy Corduroy|
|Gregg Turkington||Toby Determined|
|Niki Yang||Candy Chiu|
|Keith Ferguson||Deputy Durland|
|Jennifer Coolidge||Lazy Susan|
|Kevin Michael Richardson||Sheriff Blubs|
|Grey DeLisle|| Gorney|
Summerween Superstore clerk
|Dee Bradley Baker||Waddles|
|John DiMaggio||Manly Dan|