There are many shout outs within the icons in the upper left corner of quiz questions.
One picture is a visit card with "Call me 1-800-GRRRREAT" written on it. One of the answers on the corresponding question involves getting the phone number of the sexy tiger obsessed with health and nutrition on the front of the box.
One of the sites you can visit to get money in the library is an online poker site called "Poker Face". The opponent you face is the Fish from Nuclear Throne.
During the game show with the Prince, you can summon a robot... named Tyrelliot. This is the ship name for two of the main characters of Mr. Robot.
You can help Damien and Scott to put a wild beast they found in a cooking show called Monsterchef.
Seems like a subtle one, but Liam's quote appears to be one to Fifty Shades of Grey.
Liam: You see, I have a dark and expensive fetish. I download pop songs on iTunes.
You can kidnap a man's daughter to make him pay for your drinks when going to a bar with Vera and Polly. When you call him for ransom, he will deliver the Signature Line from Taken.
The Magazine that contains the personality quiz at the start of the game is called Teen Wolf.
Scott and Liam can be seen discussing a novel/film called Two Lights, where a girl is wanted by two guys part of different tribes: the shirtless humans and the mysterious deep-look-giving humans.
In one event, Damien has detention, and is contemplating on ditching or not. You can suggest that he can, "Cross-species, economic, and social barriers to make lifelong friends with a diverse group of students in detention and find out through silly dancing that you're not so different after all," alluding to The Breakfast Club.
Narrator: When the weekend is over, the tales of Damien's exploits as an outsider-turned-buddy echo through the halls. Rumors fly that handshakes were made up, deep secrets were revealed, and a whimsical dance scene took place in the library. By next week, people are still intrigued about why Damien is sort of frozen in the middle of the football field with his fist in the air. Damn! Did you just start a new school club?
The new secret ending introduced in the Halloween update includes Liam scrawling "This is the darkest timeline" into the dirt as he dies, referring to a phrase that was often used in Community in similar situations.
In Miranda's holiday route, if the player gets the Bad Ending, among the Polaroids of various monsters attending Miranda's funeral is one of her family. One member of which appears to be a blue mermaid wearing an eyepatch.
The hairstyle of the spirit Damien barbers for in the HAIR ending is remarkably similar to that of Funny Valentine.
One interaction features Liam and Damien talking about Slayer and monster history. Liam mentions offhandedly that Caligula and Jack the Ripper were the same vampire; this is a tidbit from the lore of Buffy the Vampire Slayer (doubly significant since Liam shares his first name with Angel).
Second Term DLC
In one event, Polly claims that the vending machine is thirsty for Calculester's shiny metal ass!
When the denizens of Calculester's virtual reality start to suspect their world is fake, the Player can propose that he puts them in another virtual reality. He puts them in a grittier reality, and the virtual people stage multiple uprisings. The whole thing devolves into a series of action movie tropes with great special effects.
Additionally, the plot of 'adult cop goes to high school as a teenager to bust a crime' is a reference to 21 Jump Street.
In the police report route, Zoe and Polly explain that the monster education system is based on the "human documentary" Saved by the Bell.
Coach implies in one cafeteria event that he's the son of Tony the Tiger.
In her special route, Hope goes through a severe existential crisis after learning she's an amalgam of the souls of three previous Hopes. By that point, the player character has only known her for, quoth, "[A] couple of days... but now you feel like if anything happened to heryou will kill everyone in this school and then yourself."
Hope's special route includes further backstory on the Coven, which includes explanation that their original Big Bad was a vampire named Angelus, but that he did a Heel–Face Turn due to a romance between himself and Joy... that still ended up not working out and landing at a point of "it's complicated", with Angelus having actually been Liam going at the time by a different name, in a Whole-Plot Reference to Buffy the Vampire Slayer.
In Monster Camp, one of the plots for Joy has you "defeating" all of her evil exes. If you manage to get together with her, the narrator explicitly says that you eventually fear becoming an evil ex yourself.
One event has Aaravi, Damien, and Dahlia dressing up like lawyers to convince the Pizza Delivery Girl that she's correctly delivered to Wolfram & Hart. Aaravi in particular dresses exactly like Franziska von Karma.
An event at the haunted house has Dahlia and Damien having a run-in with the Clueless Crew, a pack of mystery-solving teens convinced the two are shady real estate agents in disguise.
The Polaroid of Dimitri's defeat in Dahlia's RIVALRY ending is posed exactly like Kaiba's from the first episode of Yu-Gi-Oh!.
Items
The cult ring is basically an image of Bill Cipher.
One of the items is a creativity motivational poster of Bob Ross.
The "I Choo-Choo Choose You" greeting card that initiates the Blobert secret route is a direct reference to an episode of The Simpsons, where Lisa sends Ralph Wiggum that exact card.
Another direct Simpsons reference in The Gift update: the super-fun Bonestorm and the stat-sucking Lee Carvallo's Putting Challenge are fictional video games created for the Season 7 Christmas episode.
Another location, named the Secluded Village, is a small village walled off from the rest of the world. If the Attack on Titan reference is too subtle, one event even features the city being terrorized by what appears to be a blue version of the Colossal Titan (though it is very obviously just a cardboard cutout made by the village elders).
Should you visit the Space Station and choose to dress up as astronauts, you, Polly, and Scott each put on different colored astronaut outfits. However, the other, similarly-clad astronauts realize that there are one too many astronauts on the rocket, and conclude that "there must be an imposter... AMONG US!"
The flavor text at the Gothic Manor location references The Rocky Horror Picture Show, including lyrics from “Over at the Frankenstein Place” and the note that you arrived with wet newspaper on your heads.
The adorable village location is full of the types of animals and activities you’d encounter in Animal Crossing.
The Charming Village location, with its prominent maypole and visceral rites, seems to reference Midsommar.
The additional layer for this ending involves getting captured by the WTF Foundation and needing to escape. Doing so requires fighting either WTF-096, the "Shy Dude", or WTF-682, the "Hard-to-Destroy Dinosaur". Should you escape, WTF-096, WTF-682, and the Class-L personnel sent to experiment with you will join you. More characters will also be featured in the class photo, including Missingno., Slender Man, and the trollpasta character Man Door Hand Hook Car Door.
shipping issues and the pros and cons of Markapoo and Starco. Specifically he brings up the issue that due to certain events Marco might be in his thirties.