Author Existence Failure: Less than a month before the premiere of Descendants 3, Cameron Boyce (Carlos) passed away unexpectedly from a seizure caused by Epilepsy. Less than a week after Cameron Boyce's death, Disney announced that the Red Carpet premiere of Descendants 3 had been cancelled, and would donate the money that would have been spent on the event (venue rental, security, press invites, etc.) to The Thirst Project, an organization that builds wells in areas of the world where there is no access to clean water. Boyce received an award from the organization a couple of months before he died.
Before being sent to Auradon, Jay barks like a dog to scare Carlos. Booboo Stewart portrayed one of the werewolves in the Twilight film saga.
This also happens in one episode of the Wicked World spinoff: after Mal and Evie mistakenly cast a spell that makes everyone act and bark like dogs — except Carlos, oddly enough — Carlos has a lot of fun getting an entranced Jay to do dog tricks and taking pictures of him doing them.
Anna Cathcart, the actress who played Drizella Tremaine's daughter Dizzy, also portrayed a young Drizella in Once Upon a Time.
Dawson Casting: The teenaged cast is played by actors ranging from 19 to 22. Cameron Boyce was the youngest in the cast at 16 years old, which helps with making the 14 year old Carlos seem like the baby of the group.
Edited for Syndication: The first film ends with Video Credits set to Shawn Mendes' "Believe"; in later airings of the film on Disney Channel, this was removed and the beginning of the credits were moved to the beginning of the film.
Fake Nationality: Arabian Jay is played by Native American (among several ethnicities) Booboo Stewart .
This is Disney's answer to the Monster High and Ever After High multimedia franchises, which deal with the offspring of mythical/literary monsters and fairy tale characters respectively. Descendents ended up overshadowing the two to the point that both franchises were killed by the end of 2018.
This series is also another attempt by Disney to ride on the coattails of High School Musical, and arguably their most successful one to date. It helps that the two trilogies share a director.
I Knew It!: Descendants 3 confirms that popular fan theory/joke that Hades and Maleficent were a couple and that Mal is their daughter and Audrey is indeed the villain of the film.
In Memoriam: Descendants 3 is dedicated to Cameron Boyce, Carlos' actor who died of epileptic seizure on July 6, 2019. A dedication was added before the film began and the end featured various footages of him from both Disney projects and his personal home life.
Missing Trailer Scene: The beginning of the "Good to Be Bad" music video features an advertisement for VK Day as the residents of the Isle of the Lost get their applications ready. That scene was not present in the movie itself.
The two main are Bal (Ben/Mal) and Devie (Doug/Evie). Others include Jaudrey (Jay/Audrey), Jarlos or Jaylos (Jay/Carlos; the latter is the most commonly used due to Jarlos being taken by the James/Carlos ship from Big Time Rush), and Darlos (Dude/Carlos).
Another one that's gaining traction is Choug (Chad/Doug), partially due to their actors (Jedidiah Goodacre and Zachary Gibson) being best friends in real life and partially due to a couple of scenes where Doug ends up holding Chad and vice versa. For that matter, Jackary (Jedidiah/Zachary) has somewhat of a fanbase as well.
Huma is used for Harry Hook/Uma from the sequel.
Posthumous Credit: Less than a month before the third film's premiere, Cameron Boyce died of a seizure rooted in epilepsy.
The Cast Showoff: All four main villain kids sing/dance throughout the movie, their actors are singers/dancers in real life. And then there's Kristen Chenowith and her showstopping number.
Undermined by Reality: The main theme is that you don't have to be defined by your parents. Yet numerous characters are introduced and most well-known to the audience as the offspring of [insert popular Disney character]. Especially notable with Mulan's daughter who is a total copy of her.
Fans of The Blue Fairy from Once Upon A Time will recognize Keegan Connor Tracy as Belle in Descendants. Apparently before getting the role of Belle, she auditioned for Maleficent, the dark fairy, instead. Fans of her character in Once Upon A Time have long speculated her as being a secretly evil master manipulator fairy in disguise. Imagine the rejoicing if she'd gotten the part.
The film was originally not intended to be a musical, with the songs being added after Kenny Ortega officially took over as director.
There was originally going to be a character named Aziz, son of Aladdin and Jasmine but was cut out for unknown reasons. It seems Jordan takes his place in Wicked World due to being the daughter of Genie.
This Aziz character is also a bit of casting gag. The actor who played him also played in the spinoff of Once upon a time, "Once Upon A Time In Wonderland", another Disney live action shared universe show, where he played the brother of (presumably) Aladdin's genie, who was the boyfriend of Alice from Alice in Wonderland, who were fighting against the likes of Jafar. Perhaps his scenes were cut to not have people be confused to whether the television series and Disney film were apart of the same world. Belle's actress was also in the show as the blue fairy.
It's pretty clear from the staging of Maleficent's big song around statues of the other villains that never do anything, that it was originally going to have all four of them involved, but then powerhouse singer Kristin Chenoweth was cast, which demanded she get a number of her own.