Family Day (after Ben introduces Mal as his new girlfriend) is a series of tearjerkers. Almost everyone abandons the villains' kids, even the people who they'd made a real connection with (notably, Jane is uncharacteristically rude to Mal for some reason).
Also, Aurora's mother revealing just how much pain Maleficent caused her by making it so that she couldn't raise her own baby girl.
Chad didn't just abandon them, he insulted them, and pointed out their flaws. He called Mal out for stealing Ben from Audrey, said that Jay enjoyed hurting people, and called Evie a cheating gold-digger.
And the worst part is that everything he said was true. Sure, he said those things to insult them, but Mal did steal Ben from Audrey with the love potion, Jay did enjoy hurting people and Evie was only interested in him when she heard he was a prince, plus she cheated in class with her magic mirror. Though since he played with her affections to get her to do his homework, he's not one to talk.
It's even worse when you consider their Abusive Parents. Considering most kids who grow up with abusive parents live in fear of turning out like them, Chad saying Jay likes to hurt people is probably one of Jay's worst fears coming true. (And it shows on his face, to boot.)
The 'love potion cookies' scene, when Lonnie talks to the kids about how parents make cookies for their kids.
(Lonnie brings a bowl of chocolate chips to the table where Mal and Evie mix the potion/batter)
Lonnie: Wait, didn't your moms ever make you guys, like, chocolate chip cookies?
(Mal and Evie look up with sad, curious expressions)
Lonnie: Like, when you're sad, and they're fresh from the oven with a big old glass of milk and she just makes you laugh and puts everything in perspective and-
(Lonnie looks around the kitchen to see expressions of sadness and longing because of her words)
Lonnie:(curious) Why are you all looking at me like that?
Mal: (shrugs) It's just different where we're from.
(Mal looks at Lonnie, and then lowers her eyes; behind her, Evie's face takes on a look of sad realization)
(she turns to see the same sadness on Jay and Carlos's faces)
Lonnie: How awful.
The worst part of this moment is that Lonnie then provides the missing ingredient for the love potion - a tear of real human sadness. Lonnie was so heartbroken by the thought that four kids - basically strangers to her - didn't have parents that loved them that she cried for them.
Re-watch that scene; then think about the burned-out-village scene from Mulan. Lonnie does take after her mother: they're both gut-punched in their youth by proof that villains hurt children.
During their date, Ben tells Mal that he loves her and asks what her feelings are; she tells him that she doesn't know what love is. The real sadness kicks in when you realize later that Ben's not under the love spell when he tells her that he loves her.
Doug's demeanor towards Evie after Family Day. He wants to go to her but is forced by Chad to stay away. The way that he sits - not looking at Evie, but unwilling to look at the other kids - shows that Evie was probably one of his only friends.
This is particularly hard to watch when you remember the episode of "School of Secrets" that shows Doug is close to the rest of the dwarves in what appears to be an Honorary Uncle fashion (he refers to "Uncle Doc" and "Uncle Grumpy" when talking about a care package the dwarves sent), which implies that he's probably also close to Snow White. Yet if they have kids at Auradon, they ignore Doug at best and bully him at worst. Ouch...
The night before Family Day. The main four are thinking about how much they've grown as people since they got to Auradon Prep and wondering if they should go through with the theft. Mal is making the love potion antidote and sings a reprise of 'If Only'. She cries a tear of real human sadness, which is a big deal considering she said earlier that she never cries.
'If Only' seems to made of this, especially the line:
Will you still be with me,
When the magic's all run out?
A bit more subdued, but Chad being a jerk counts. One has to wonder how heartbroken Cinderella must be when she learns of how her own son behaves.
It's not only bad because of a jerk, but specifically because he gets other people to do his work for him, is nasty to them if they decide not to, and isolates them from people who care about them. He acts like her step-family acted towards her.
The fact that it's hinted that Dude is the first thing in Carlos' life that makes him feel like he's worth something. Even if they didn't mean it, Mal, Jay and Evie made their honorary little brother feel like they just want to use him; can you imagine how bad they'll feel if they figure that out?
During the 'Evil Like Me' number, Mal keeps switching between being reverent of Maleficent and being fearful of her. There's also the fact of how, despite Maleficent saying that Mal will be right by her side when the villains win, she's clearly running the show and is actually rather dismissive of Mal. Seeing as how the whole number is very likely a product of Mal's mind, it shows that Mal knows Maleficent doesn't actually care about her, but clearly wants to think otherwise.
Anyone whos ever felt bad about their appearance can feel for Jane as her self-esteem is kicked around; When she meets Mal in the bathroom she displays her insecurities for the first time and Mal preys on them while pretending to be a friend, then after Mal undoes her spell after Jane makes a mean comment all of Janes friends laugh at her prompting her to run away in embarrassment. Even Snow White takes a small jab at her at the coronation. All this feeds into her anxiety so much that she steals her mothers wand and accidentally opens the barrier and releases Maleficent. She sits with this guilt until Carlos and Jay invite her to dance.
In a meta sense, the whole plot is one big tearjerker. The Heroes go Knight Templar on the Villains, revive them, and banish them to what is pretty much an island ghetto without basic human rights (technology, food, even toys for the kids if the second film is to be believed) while adapting an All Crimes Are Equal policy (with only a few such as Aladdin are pardoned from). Even a generation on, hatred and racism continues to prevail on both sides, with very few people in Auradon (like Ben and Lonnie) even treating those born after the purge with humanity. We already know that the Villains take their frustration out on their children, which only adds up to how they're forced into a life of evil and hatred because an enemy faction treats them as Always Chaotic Evil. It is almost like a fantasy version of the real-life conflicts between North and South Korea, and Israel and Palestine.
Even after everything they did in the film, Wicked World shows that the Villain Kids are still mistrusted by many of their classmates, several of whom manage to be extremelyInnocently Insensitive (see Ally's speech about why she's asking new-to-magic Jane to magic up a vehicle to take the girls to the dance instead of Mal - to be fair, she is clumsy and causes a lot of bad luck to happen). The worst part is that other Villain Kids like CJ or Zevon take advantage of it and only strive to further the divide for their own benefits by making the redeemed Villain Kids' (specifically Mal's) life even more miserable.
In Wicked World Episode 15 "Carpet Jacked", Ally spends several minutes casually insulting Mal while trying to explain why she wants Jane to magic up the group's vehicle. Not to mention the fact that Mal and Evie only care that Jay and Carlos didn't bring the carpet they were supposed to, not about, you know, whether the guys are okay or not (it turns out they are but that wasn't revealed until several episodes later).
"Odd Mal Out" has Mal discovering that she's the only kid who can't get her family jewel due to Maleficent hiding on the Isle; Mal is devastated. Then later on when Mal starts actingstrange, just about everyone sides with the suspicious Audrey, completely destroying Mal's new life, much to the obvious dismay of Evie, Jay and Carlos.
Finally, "Trapped" has Audrey realizing she hurt Mal so bad when she finds out what really caused Mal to act so evil, and feeling completely awful that she was hostile towards her because of that misunderstanding. What makes it sadder is that Audrey is racked with guilt knowing that, in the previous episode, she had abandoned Mal and said something she can't take back.
In the sequel song "What's My Name?", there's a line sung by Uma, Ursula's daughter. It goes 'Leaving us here will be the last regret' because it emphasises once again that the young people on The Isle Of The Lost are abuse victims who just want out of their abusive environment. Because the people of Auradon cant pretend any more that they dont know what its like for the children of The Isle and the fact they didnt immediately try and find a way to remove the children is super messed up. (from this tumblr:http://franinconverse.tumblr.com/post/161864466034/the-most-important-line-in-whats-my-name-is)
One brief scene a few moments before "Chillin' Like A Villain" has Carlos, Jay, Evie, and Ben walking through an alley to find Mal. When Evie passes by, two children run up to her to take her valuables. Evie yells at them to stop, before they frown and stare at her in dismay. Evie, out of sympathy, lets them take one of her things, and sadly watches them run off, giggling, before catching up with Carlos and Jay. Might be short, but it's really effective on showing how the children trapped on the Isle of The Lost are suffering. You can tell that they don't steal out of malice, but because it's all they know to do to get by.
When Ben is captured by Uma, this conversation between them follows.
Uma: My mom doesn't care about me. Well, not unless she needs someone for the night shift.
Everything about Dizzy Tremaine! The poor thing is an innocent in an island full of Villains and their rotten offspring. She's too little to fight back against other VKs who bully her, treats everyone kindly, and only wants a life with happiness and love. Her situation demonstrates the clearest how horrible leaving kids in a Wretched Hive was on Auradon's part.
Mal: She's gonna be okay.
Evie: Yeah, but she could be so much more.
Worst of all, it's hinted that once Cinderella was out of the picture, Lady Tremaine transferred her abuse to her biological family (which, sadly, happens all too often in Real Life). Dizzy says that Lady Tremaine has gone from being a Wicked Stepmother to a Wicked Grandmother, and that she makes her "scrub and scour". And, unlike Cinderella, Dizzy and her mother (and aunt) are prisoners on the island and have nowhere to escape to. Ouch.
Ben, under the influence of love magic, rejects Mal in favor of Uma at the royal cotillion, publicly humiliating her and breaking her heart. What makes it worse is that Mal is willing to go along with it, believing that he'd be better off without her, and is too shocked to realize something's wrong.
The entire scene where Ben discovers Mal's spellbook in a picnic basket, and all the enchantments that she's been using to try and keep up with the demands of being the King's girlfriend. While the first film has him so nonchalant and amiable about being put under a love spell, he is much less kind and considerate this time, showing one of his rare moments of anger, revealing it was a one-time deal.
Ben:Are you trying to spell me?!
Made even worse by Mal's heartbreaking explanation that she can't handle the pressure without magic because she feels like a fake. It really deconstructs the idea of rags to royals "fixing everything" in a very vivid, relatable way for everyone. One only has to wonder how the other rabble-to-royals like Aladdin, Eugene Fitzherbert, and Robin Hood have managed...
Ben's anger over Mal's attempt may also tie into the use of the love spell - love spells (in fiction) are often seen as fun-lighthearted things, right up until you remember that it is a concoction that utterly negates the spelled person's free will - Ben might have been okay with Mal's love cookie because she tried to undo it afterwards and clearly felt bad, but here she is, in what is supposed to be a fun date, casting a spell that (if you listen to Mal's words) will ERASE BEN'S MEMORY OF THE ARGUMENT THEY ARE HAVING. No matter how nice you are, seeing someone you love be completely unfettered at erasing your memory to resolve a minor argument would make you upset. Ben's had his free will ignored by Mal before, and no matter how much he loves her, you can understand why he wouldn't want it happening again.
When Mal (who is having a breakdown over the upcoming cotillion) talks to Carlos about missing her villain days:
Mal: Carlos, don't you ever miss screaming at people and watching them run away from you?
One can feel bad for Audrey when Queen Leah chides her for Ben dumping her and choosing Mal as his queen, from saying their family's status and years of planning ruined to how her mother Aurora could still "hang on to a prince" while asleep but Audrey couldn't. You know, things that Audrey would have no control over anyway let alone no young girl should be responsible for. It feels not too different from how the VKs felt fear and pressure to not fail their parents' plans in the first film and how Maleficent initially reacted (and how the other Villain parents might have) when Mal and the others did not follow through.
If that weren't enough already, just watching her performance in Queen of Mean shows Audrey's vulnerable side; She strove to be the best princess she could ever be, and she wanted to make her family proud, but she's been pushed around and burned far too many times, and out of all her losses, losing Ben made her feel like a failure to her grandmother, and that just broke her. It is heartwrenching enough that you can just feel her pain and sadness during her performance.
When Mal reveals to the other VKs that she lied about allowing all the Isle kids coming to Auradon and that it was her idea to permanently close the barrier. They are all understandably upset, but what's worse is that Uma isn't so much angry as much as disappointed like deep down she knew trusting Mal again would lead to this, while Harry turns to Ben not to get in his face and antagonize him, but to solemnly, rhetorically ask if they're going to be thrown back onto the Isle again. Meanwhile, Celia starts to cry because it means with her staying in Auradon that she'll never see her father again (who she's shown to have an actual close relationship with). Evie tearfully does all the talking bringing up that they're breaking their promise (and duty) to make change for the other Isle kids, as Jay and Carlos can't bring themselves to say much else. Even Ben doesn't add any additional input or come to Mal's defense since he wasn't happy with the idea either.
Evie, finding Doug in a state of enchanted sleep, has an entire solo about how unsure she is whether or not she can revive him with True Love's Kiss. She knows she cares for Doug, but isn't sure if it's true love she feels, and she's even more unsure of his feelings; they've never actually said if they love one another before. She's so uncertain, and so fearful that her feelings and his won't be strong enough for it - or their relationship thereafter - to work, that she's hesitant even to try to awaken him, lest she lose this young man who means so much to her. It works.
Cameron Boyce, who played Carlos, passed away in July 2019, which means not only was Descendants 3 the last time he would be on Disney, it would be one of his final TV and film roles period. Quite an unfortunate way to end the trilogy.
His death alone is sad in itself (he was only 20 years old and died in his sleep from a seizure due to epilepsy), even sadder than any tearjerking moment in Descendants 3 but seeing the rest of the Descendants cast and crew devastated from his death, paying many tributes to him, and vowing to continue on his legacy through his charity work and promoting kindness, shows how close and how much of a second family they were to each other.
Want something even sadder? Mitchell Hope (Ben's actor) apparently called Cameron's phone 85 times and texted 13 times, thinking it was a fake story.
The night of the Descendants 3 premiere, Disney Channel bookended the movie with dedications to Cameron. The beginning was preceded with this title card, and after the end they played a montage with clips of his life. Very few eyes stayed dry in the audience.