Soos' poster "HE'S GOT ATTI-CUBE" on the door of his room has a COOLCUBE logo at the top that is a cube made of C's, a parody of the Nintendo GameCube whose cube is made of G's. The running cube on the poster also resembles a Rubik's Cube and 7-Up's old mascot, Cool Spot.
The fact that Giffany killed her creators after becoming sentient is a nod to GLaDOS from the Portal series. Giffany's animation depicting a bunch of stick figures at computers greatly resembles similar animations played in Portal 2.
On Giffany's screen, the binary code means "SPACEJAMTWO." This is a reference to the film Space Jam and how it may be getting a sequel sometime soon.
When Soos mentioned that Giffany's father is the "octopus man," this is the reference to the tentacle Hentai.
Soos says he doesn't know whether to pronounce Giffany's name as "Giffany" with a hard G, or "Jiffany." This is a reference to the common internet dispute about whether "GIF," a file format, is pronounced with a hard or soft G.
The cryptogram at the end slide is a parody of the theme song of the DiC/CWi dub of the anime Sailor Moon. "WINNING HEARTS BY DAYLIGHT! / POSSESSING ROBOTS BY MOONLIGHT! / HER EMOTIONAL BAGGAGE IS A REAL FRIGHT! / SHE HAS THE ONE NAME GIFFANY." Similarly, the first four lines of the DiC/CWi's Sailor Moon theme song are "Fighting evil by moonlight / Winning love by daylight / Never running from a real fight! (or 'With her Sailor Scouts to help fight' in a later verse) / She is the one named Sailor Moon!"
The show "Ghost Harassers" is a reference to the movie Ghostbusters. Dipper also mentions "bust[ing] ghosts" several times in the episode.
One of the verses in the exorcism is "ain't afraidus no ghostus," which is reference to Ghostbusters theme, in which one of the lines is "I ain't afraid of no ghost."
Used to be About History Channel is a reference to the History Channel. The logo is also similar to the History Channel logo. The name is also a reference to how the channel very rarely runs any actual historical documentaries anymore.
Preston's line "you are my possesions! Obey me!" is very similar to a phrase from Sasha from the game Pshrconaughts, "You are my possessions do as I command"
The basketball player is a spoof of the Oregon Ducks, a college team for many sports.
In the scene where Dipper and Pacifica are hiding from the Lumberjack ghost, a painting is seen on the wall depicting a duck hunt. The way in which it is presented is an allusion to Nintendo'sDuck Hunt from 1984.
Furthuring the Apple Computers / Fiddleford H. McGucket connection is the fact that his and Steve Jobs' houses are virtually identical.
The "Mothgar" poster in Stanley and Stanford's childhood room is based on the American theatrical poster for the 1961 film Mothra.
There is a poster in McGucket's old home, which shows a colorful, bitten-off strawberry similar to the Apple logo, and the words "Ponder alternatively," which is a play on Apple's slogan "Think differently."
College Ford was shown in learning progression montage. During that montage, two posters are shown on his dorm room wall. They are the iconic Nicola Tesla and Carl Sagan, two great thinkers and doers of recent history.
The title and the game in this episode is a parody of the popular role-playing game Dungeons & Dragons.
Like D&D, Dungeons, Dungeons, and More Dungeons use an assortment of polyhedron dice.
The 38-sided die is based on, and resembles, the 20-sided icosahedron die used in Dungeons & Dragons to resolve most rolls. There are no 38-sided die used in any real life RPGs; the closest is a 30-sided die, but this an unusually rare and impractical type of die.
Dipper's mentioning Dungeons, Dungeons, and More Dungeons' '90s marketing campaign is a reference to how the company of D&D, TSR Inc., aggressively marketed D&D in '90s to keep up with the growth of other RPGs on the market, and many poor business decisions that drove TSR Inc. into bankruptcy.
Stan describes Duck-tective as: "A TV show that has big mystery elements and jokes that go over kid's head's" which is ironically what Gravity Falls is.
When the Pines family along with Soos and Grenda show disappointment for the Duck-tective season finale's plot twist. Soos mentions predicting it a year ago which is a reference to "Stan's twin brother theory" where fans of the series predicted that Stan had a twin brother, which was later confirmed in "Not What He Seems."
"We all know where we were when we learned Duck-tective was shot" is a reference to how people say that they remember where they were when they heard that John F. Kennedy was assassinated.
The Hot Elf saying "Excelsi-whatever" is a reference to Stan Lee's "Excelsior!" line.
The fantasy names posted up on the boards in the living room by Dipper and Ford are all parodies of names from "The Flight of Dragons," an animated movie adaptation of Gordon R. Dickson's book "The Dragon and the George." (Jason Ritter's father, John Ritter, was the voice the protagonist, Peter Dickenson, in the movie.)
Gorbasch -- there's a human/dragon character named Gorbash in both the book and movie.
Smerghol -- Smrgol, another dragon from the movie adaptation.
Omhadawn -- the evil wizard Ommadon, from the movie adaptation.
Grunkle Stan's campaign slogan "Yes We Stan" parodies Barack Obama's 2008 tag "Yes We Can."
The opening of act three is a parody of the "Staying Alive" scene from the film Saturday Night Fever.
Stan's "One does not simply" meme is a reference to the popular internet meme of the same name, both of which are based on a quote from the first Lord of The Rings movie, in which Boromir says, "One does not simply walk into Mordor."
The monitor worn by Bud Gleeful is based off of Krang from Teenage Mutant Ninja Turtles.
The poster in Gideon's cell of a picture of a cat hanging onto a branch that reads "HOLD ON TO THAT BRANCH OR DIE, CAT!" is a reference to a well-known poster of a cat hanging from a branch that reads "HANG IN THERE."