Having never shot down Toothless and not having gained the respect of his father and Berk, took its toll on Hiccup. Then he was arranged to be married to Astrid and instructed to uphold his duties as the chief's son and produce an heir. Now he has a daughter who has to face the same prejudices as him. It's about time that things change on Berk for the better.
What Lies Beneath provides examples of:
- Abusive Parents: While Stoick's parenting is built more on ignorance than malice, at best he's neglectful, prioritizing his chiefing over actually looking to his son's needs, continually postponing taking any time to train Hiccup to fight under the belief that he wasn't ready. At worst, he's emotionally abusive, either making Hiccup think that it was somehow Hiccup's own fault that Stoick had no time for him (albeit by accident) and misinterpreting Hiccup's silent pleas for help as him being stubborn. It takes years of Hiccup's aloofness, scolding from his daughter-in-law and seeing how radically different a dad Hiccup is to Zephyr for it to really sink in.
- Adaptation Relationship Overhaul: In-canon, Hiccup and Astrid's relationship was never really established until she discovered Toothless. Here, they were friends as children before "[their] interest took [them] in different directions". While their canon counterparts eventually Marry for Love at the end of the third film in their twenties, here it was arranged for them by their parents when they were in their late teens, their feelings developing at some point after the ceremony.
- Adaptational Angst Upgrade: In canon, Hiccup usually responded to his village's scorn with a clever quip and went on with his day. Here, continued psychological abuse from the villagers and his father turned him into the quiet, cynical and anti-social young man he is today.
- Adaptational Nice Guy: Mildew in canon was a Hate Sink who was so unlikable, his house was built outside of the village because nobody could stand him, and he later selling out Hiccup to the Outcasts. Here, when Jerrik implies that Hiccup and Zephyr's death was a net-gain for the village, Mildew pitches in when villagers start responding with kind words, saying how Hiccup volunteered to help when Fungus when he was stuck in the well and Zephyr would keep him company.
- Adult Fear: The Night Fury had to leave his mate and one of his children in captivity to get himself and his other two children to safety.
- Altar Diplomacy: Hiccup and Astrid were pushed together in their late teens by their parents. They eventually grow to like each other anyway.
- Ambiguous Disorder: Hiccup has no interest in socializing and avoids anyone who isn't family, and even then he only likes being around Astrid and Zephyr. When multiple people try to strike up a conversation with him after Astrid shames everyone for mistreating him, he nearly has a panic attack and is unable to do anything for the rest of the day, all signs pointing to Hiccup having some form of Social Anxiety Disorder.
- Be Careful What You Wish For: Stoick and Gobber constantly told Hiccup that he should stop being like himself and start being less talkative and in the way. What results is Hiccup becoming reclusive, giving up on his hobbies and doing nothing but his scheduled task. This does not go unnoticed by Gobber and Stoick, and it isn't until years later does it really hit Stoick just how badly he hurt his son."You can't have it both ways." He said in an unnervingly steady, yet firm voice. However, tears started to run down his cheeks as he spoke, "You told me to stop being me. Everyone told me to change. Now that I have?"
Without warning Hiccup swept his arm across a table, sending tools flying everywhere in his sudden rage. Stoick and Gobber remained still, shocked by Hiccup's behavior.
"You're telling me you prefer the the screw up of Berk over this?! I'm still not good enough." He pushed past the shocked men toward the entrance, then turned for one final word before leaving. "Make up your damn minds! I don't know how much more of this I can take..."
- Break the Cutie: Hiccup hits the Despair Event Horizon when Stoick point-blank tells him that he should stop being himself, turning Hiccup borderline-suicidal in the ring and destroying what little of a relationship they had.
- Daddy's Girl: While both her parents are Good Parents, Zephyr is particularly close to her father.
- Everyone Has Standards: When everyone thinks Hiccup and Zephyr both died in a raid, Jerrik tactlessly remarks that mourning them isn't worth it and that Astrid's pregnancy secures an heir. While most of the village thought that Hiccup was a poor viking and Zephyr took after him more so then they had liked (even though she's only three-years old), the look on everyone's faces makes it clear that his words are beyond appropriate. When Astrid responds with Unstoppable Rage, no one even thinks to stop her, Stoick stopping after she got a few hits in with a plank of wood first. When Jerrik tries to justify his words, various other villagers contradict him with kind words about them.
- For Want of a Nail:
- Unlike in canon, Hiccup does not see Toothless after shooting him down and freeing him for years. Because of this, Hiccup never learns how to tame dragons, he never learns how to pacify dragons in the ring and he does not become the one to kill the Monstrous Nightmare.
- Toothless does not lose his tail-fin from the Mangler's net, letting Toothless leave Berk.
- When Stoick tells Hiccup that he will begin dragon-training, he actually notices when Hiccup tries backing out of it. It escalates until Stoick point-blank tells him to stop being himself, causing Hiccup to do just that.
- Good Parents: Hiccup and Astrid ensure that Zephyr is loved and supported, with Stoick in particular noting that Zephyr explicitly stated that she always knows her father loves her.
- Happiness in Slavery: 'Happiness' may be an overstatement, but the Night Fury's thoughts reflect that he succumbed to the Red Death's control because it was easier to feel some sense of belonging after the loss of the rest of his family.
- Jerk with a Heart of Gold: When Jerrik tries making Hiccup and Zephyr's (supposed) deaths look like a triumph, Mildew is one of the villagers who stands up for them, mentioning that Zephyr would keep him company while Hiccup helped him fish Fungus out of the well whenever he fell down it... though he insists he still didn't like him.
- Kids Are Cruel: Berk's children take a cue from their parents and use Hiccup's bad reputation as an excuse to bully Zephyr. Unlike Hiccup, Zephyr has the self-confidence to defend herself, as inherited from her mother.
- Lack of Empathy: When everyone thinks that Hiccup and Zephyr perished when their house caught fire during a raid, Jerrik tactlessly says that they won't have to worry about securing an heir since Astrid is pregnant and hopes that it take more after Astrid than Zephyr did. Astrid responds by going from bottomless grief from wanting to murder him in an instant and no one stops her until she gets a few hits in.
- Lethal Chef: Like her mother, Zephyr isn't that great of a cook, her instinct when it comes to making soup is to throw whatever ingredients they have into it.
- Masculine Girl, Feminine Boy: Astrid and Hiccup have this dynamic. Astrid is the fighter of the two and is a more natural leader, willing to threaten anyone who says anything bad about her family. Hiccup however acts more as a House Husband that takes on more initiative in parenting Zephyr and prefers the seclusion of domestic life and forging to avoid the rest of the villagers.
- Morality Chain: Just meeting Hiccup disrupted the Queen's hold on the Night Fury, so he remained with the pack out of choice rather than her control.
- My God, What Have I Done?: Astrid didn't do anything directly, but she is disturbed when she finds one of Hiccup's notebooks and reads about how he thinks that nobody wants him for anything more than fathering the next heir, rather than appreciating him as a person.
- Shaming the Mob: When the village accuse Hiccup of not contributing to the village and call Zephyr "as pathetic as her father" when Astrid's yelling accidentally upsets her, Astrid gives a scathing "The Reason You Suck" Speech right back."You ungrateful jerks! Hiccup forges the best weapons on Berk! He is not useless. So what if he decided to play a different role? Why should he want to lead you lot of degenerate boneheads anyway?"
Some of the Berkians looked scandaled, others slightly ashamed, some slightly confused by the big words.
"How dare you insult my daughter? A three-year-old, little girl? Of course she isn't going to flourish, not when she is treated the way she is. You can't judge her before she's even had the chance to show what she has to offer. You're doing the same thing to her that you did to Hiccup. Don't try to deny it. I know that deep down you all know. Hiccup is the way he is because of us! He put up a bunch of walls and hides himself away, because he never received a kind word from anyone. I am so grateful that Zephyr has Hiccup because he will never allow her to feel the way he does. And so help me, if you drive my daughter to the same depths of despair as my husband... I will come for your unworthy, pathetic souls and hand them over to the ruler of Helheim himself!"
- Token Good Teammate: Eret is shown to be this in a scene looking at the dragon trappers, as he only captures the dragons but makes it clear that he won't tolerate abusing them, leading to him forming a discreet alliance with Valka to undermine Grimmel's own efforts.
- Trauma Conga Line: When he was young, Stoick told Hiccup that he wasn't going to train him because he was a late-bloomer and wasn't ready to begin training, responding to Hiccup's reasonable assertion that that was the whole point of training with a Because I Said So. Later, Astrid breaks off her friendship with Hiccup after Finn is killed by the Flightmare and Snotlout and the twins beat him up because they think he was the reason she ran off upset, being banished from going anywhere near any of them the next day.
- You Are Better Than You Think You Are!: Astrid encourages Hiccup to recognise that he has value and other people see him as important by mentioning the way other people praised his work when they thought he might be dead after an earlier raid.