Also how in the cave he switches from "nice" to Faux Affably Evil when they find a door to Grimbeard's real treasure.
Grimbeard the Ghastly's booby traps.
His coffin cut off Alvin's hand. Even if Alvin is evil that is a gruesome trap.
The stinking crystals on the Isle of the Skullions, located inside the treasure chest. Skullions can't see or hear, but they can SMELL, and the smell is strong enough to wake them up . . .
The Strangulator in the underground cave. Tentacles made for strangling, and a poisonous needle.
The Skullions chasing down Hiccup, who's too small to outrun them and too scared to scream for help. Imagine being chased by creatures with long claws to cut your tendons, and who will hunt you through hollow tree trunks, with Eyeless Faces and snuffling sounds . . .Good thing Stoick noticed in time and saved his son.
When the Outcasts take over the Hooligan ship after the treasure is obtained, they plan to put all of Berk into slavery. All except the Chief and his Heir; they are eaten.
How to Speak Dragonese
Toothless getting captured, and trapped in a dark place.
The Sharkworms in the Roman arena, with the audience cheering as Hiccup lowers himself into a barrel to face them.
The Venemous Vorpent, a dragon whose bite is fatal if not cured by a potato in several months. Fishlegs is thought to be bitten, but Hiccup actually receives the bite.
Some Fridge Horror hits him and the reader when Hiccup was revealed as the Viking with Vorpentitis. If Hiccup hadn't gone on the quest, he would have died.
Norbert the Nutjob locking Hiccup in a tiny cage, invoking Exact Words to let him live but keep him imprisoned.
The Squealers, worms that release a sonic screech, for Toothless because the screech can kill a dragon his size. When Camicazi sets them off by accident, Toothless nearly passes out.
How to Twist A Dragon's Tale
Most of Humongous's attempts to murder Hiccup even if he saves him at the last minute each time. The highlight has to be his last, where he stands over Hiccup's bed debating whether or not to kill him.
His first one, setting up Hiccup in an axe fight with Snotlout and giving Hiccup a wooden axe is a nice Call Back to How To Be a Pirate.
The Exterminator dragons, period. A thousand of them are coming to wipe out the Archipelago.
Alvin defeating Hiccup in their duel by tripping him and interrogating him about the Fire Stone. It's the moment where we realize that Hiccup is just a kid and Alvin is an adult, and Pick on Someone Your Own Size is in effect.
A Hero's Guide to Deadly Dragons
The Hairy Scary Librarian. Two swords, one crazed mind who hates thieves, and training from Flashburn.
Driller Dragons. All muscle and drill, no brains, and quite willing to kill easily.
Madguts the Murderous. He doesn't speak and doesn't have to; if you steal from him coughBigBoobiedBerthacough the best you can hope for is slavery if he's in a good mood, and execution if he's in a bad mood.
How to Ride A Dragon's Storm
When Madguts's dragons kidnap Hiccup, Camicazi and Fishlegs during the swimming race. Fishlegs can't swim well, so Hiccup is trying to keep him afloat. Then one by one they get dragged down into the deep . . .
The Wanderers catching Hiccup as he falls into the hold. Think of it: no light except from the hatch above, being held down by a dozen angry slaves. and threatened with death. Does This Remind You of Anything??
On top of that, the grandmother gives him the Slavemark as a reminder of his bargain with them.
Polar Serpents in the North Pole. Chasing Hiccup, who can't reason with them.
Madguts's prize after "winning" the swimming competition: demand that Stoick and Bertha be sacrificed to the Sky Dragons, in addition to receiving the Hooligan and Bog Burglar lands. Thank goodness Hiccup ended up being declared the winner instead . . .
How to Break A Dragon's Heart
Ug the Uglithug and his men ambushing the Hooligans at night when the Hooligans set up camp on their territory.
The witch Excellinor, Alvin's mother in the tree. Even though she saves Toothless's life by removing all the inedible objects he's swallowed, she is definitely evil, shown when she expresses her desire that Alvin will become king.
Moments from the story of Hiccup Horrendous Haddock the Second
Adult Fear for Chinhilda, Grimbeard's wife, when her husband takes away their runt baby to leave him on the hillside. He refuses to kill her when she attacks and begs to know where the baby is, so she rides off in a boat to find Hiccup II. And never does.
Grimbeard the Ghastly stabbing Hiccup II during a chess game and peaceful dragon demonstration, because Hiccup's brother Thugheart convinced his father that treachery would happen. While How to Train Your Dragon is a story about forgiveness and second chances, it's horrifying that Hiccup II begs Furious not to kill his father in turn, and more horrifying that the incident plus a few centuries in chains turned Furious into a Woobie, Destroyer of Worlds.
Thugheart insinuating Hiccup II would lead a dragon rebellion to cover up Thugheart's actual rebellion. He was already Grimbeard's heir but was furious that Hiccup II was his father's favorite child. He destroyed his familyFor the Evulz
The sheer unfairness that Hiccup II got a stab in the heart for supposed treachery while Thugheart and his followers got exile for genuine treachery. Sometimes you wonder if There Is a God! in this series, or if the Norse gods are just apathetic to Viking cruelty.
Fridge Horror about how Chucklehead, Grimbeard's only son to escape the drama, had to cope with how war and betrayal tore his family apart. There Are No Therapists in Viking times, and he was tasked with being chief of small Berk. And worse, we never hear his story, probably because most Vikings can't write . . .
The witch as she tells the story revels in the tragedy, and plans to crown Alvin king.
The Dragon Furious laying waste to the Isle of Berserk, as part of his revenge for being chained for thousands of years, and his promise to never let Hiccup reach adulthood.
How to Steal A Dragon's Sword
The Wodensfang under the school.
All the Vikings except Fishlegs turning their backs on Hiccup.
How to Seize A Dragon's Jewel
Valhallarama and Hiccup's duel in the woods, which becomes Adult Fear for Val when she recognizes her son. Although the prose plays the realization for laughs with Toothless and the Wodensfang dropping a tree trunk on her head, it's a Harsher in Hindsight moment that she didn't realize what was happening at home.
The Beast under the sand, and how it eats its victims.
How Hiccup defeats it: playing dead long enough for it to swallow him legs first, so that he can stab its weak point, losing a toe in the process.Eughh
Valhallarama kidnapping Hiccup the second time, snatching him off Windwalker's back. For kids out there, it's a shocking moment when you think your parents are betraying you to the enemy.
How to Betray A Dragon's Hero
—>"WHERE IS MY TOOTH"
Hiccup getting bitten twice, in his left arm to boot. Hissword arm.
Camicazi trapped in a dark place, and crying though Bog Burglars don't cry. Nothing Is Scarier till we see where she's locked: a chained-up box.
Snotlout betraying Hiccup to the witch, and the fallout for the two of them. Even for readers that see it coming, it's quite a kicker.
The witch's plan to break Hiccup: chain him up, drop him into the cold sea filled with carnivorous Winterfleshers (piranha-like dragons that would "certainly attack a chained child"), and bring him up to ask for his parents' hiding place. Either his spirit would break, the Winterfleshers would mangle him beyond repair, or the freezing ocean would kill him.. If not for Hiccup's plan B, he may not have survived the Cold-Blooded Torture.
Hiccup's lips are blue at the end of it, and he nearly succumbs to hypothermia after escaping and rescuing Camicazi. Thank you for warming him up, Windwalker!.
Snotlout dueling Hiccup after Hiccup has just drowned the Vampire Spydragon that bit his left arm. Normally Hiccup is the best swordsman in the Archipelago, but the Spydragon bite leaves his left arm paralyzed an unusable for battle so he has to use his right arm. As a result, though Hiccup puts up a good fight, Snotlout defeats him and has him at swordpoint.
The scene could serve as a trigger for those who suffered bullying, Domestic Abuse or Abusive Parents, because during it Snotlout is blaming Hiccup for being born, for making Snotlout act like a bully rather than a hero, and Hiccup is apologizing for it. That's right, Hiccup is apologizing for his cousin trying to kill him since they were young Hooligans. Where to start with the Unfortunate Implications?
The falling scene, especially once they pass the peak of the mountain.
The Red Death's introduction. You HAD to feel seriously sorry for that poor unfortunate Gronckle.
Lets not forget about the unlucky Hideous Zippleback that, too, got dragged down and eaten by the beast afterwards.
The Red Death, a dragon the size of a very large hill, taking flight and ascending into the sky after Toothless and Hiccup. Having it emerge from the earth is terrifying enough, but seeing something that looks like the unholy spawn of Fenrir and Jörmungandr take to the air and disappear into the clouds left one awestruck. That's the point where the Vikings probably thought that Ragnarok has started and the world was about to break.
Not to mention seeing it breathe fire when it can't keep track of where Toothless is flying. When most of the other dragons have been shooting quick bursts of fire, watching the Red Death freak out and unleash this continuous stream of flames through the sky is just terrifying.
Lets also not forgot the things teeth. While all the dragons in the film have lots of teeth that are proportionately very big, its stand out more thanks to how huge it is and that it has a mouth like a theropod.
Also some of the details on the various dragons in the handbook.
Hiccup: Eats its victims... burns its victims... buries its victims, chokes its victims, turns its victims inside-out... Kill on sight.