- The Screaming Death, introduced in "Tunnel Vison" is a mutated Whispering Death, second only to the Red Death in terms of size, and one of the most dangerous dragons seen. It's even in-universe Nightmare Fuel for the dragon riders and they can be seen clearly terrified every time it shows up.
- Dagur, first met in "Twinsanity" casually recounting what are probably his father's last words, begging Dagur to put down an axe. And then offering to help Hiccup off Stoick. Hell, Dagur in general, a violence-prone teenager who commands an armada and is hellbent on hurting the heroes, even taking command of the previous villain's men by seemingly dispatching him. Teens Are Monsters indeed.
- Race to the Edge gives us the Death Song, a dragon that lures other dragons in with its siren song and then imprisons them in hardening amber so it can easily devour them. If the pile of bones from its past victims isn't bad enough, we see it carry various dragons off to their doom on screen. What's more, the Deathsong is STILL OUT THERE. Last we see of it, the gang sealed it in a cave, but Hiccup himself states that it might not hold. To add salt to the wound, it's likely that there's an entire SPECIES of it.
Tuffnut: Now that they're on the same team, what's stopping them from BOTH eating us?
- A later episode shows that yes, it did escape, and not only that, the riders have to help it raise another of its species. The heartwarming-ness of the Deathsong adopting Garff is offset by the fact that there are now two predatory dragons living on a bone-littered graveyard island. Best summed up by Tuffnut:
- In Race to the Edge, the Dragon Eye that Hiccup finds initially releases gas that causes Tuffnut to go into a seizure. No one bats an eye, but anyone who has witnessed seizures would find it troubling to see.
- Race to the Edge's two-parter, "Maces & Talons", has an outgambitted Hiccup screaming out of frustration of losing the Dragon Eye to Viggo. What makes this more unnerving besides hearing the normally happy-go-lucky guy scream like a berserker? The fact that his scream sounded eerily similar to Drago's scream.
- Also in "Maces & Talons", the way that Viggo has one of the Dragon Hunter mooks disposed of. We don't see it, but the scream is truly nightmarish.
- "Buffalord Soldier" gives us another for Viggo— not only was he willing to spread a centuries-old plague just so he could get rich off of a cure, he infected one of his own fishing ships to begin the spread.
- The Grimora — wriggling little worms with a head consisting of nothing but teeth, too small to easily see, that make dragons go crazy. You shudder just looking at them and the way they move, let alone watching what they do to the dragons. Thankfully they are noted to be quite rare, that island just had a lot of them for some reason.
- Literal case in "Not Lout" where Spitelout gives Snotlout a talk about his position. The result? A rather trippy nightmare for Snotlout where the rest of the Riders find him reduced to a beggar and end up rubbing it in with various (out of character but based on Snotlout's perception) ways, such as Dream!Heather claiming she would've married him or Dream!Gustav having claimed Hookfang as his dragon.
- The Submaripper. Aside from its opening act being to sink three trading ships with its whirlpool breath, that thing is big enough to eat a Scauldron (which it nearly does). And if whirlpools weren't enough, its Vacuum Mouth can suck down aerial opponents from underwater.
- In the same episode, anybody claustrophobic or with a fear of drowning will find Hiccup nearly suffocating deep under the ocean in a capsule the size of a cauldron terrifying.
- The Shadow Wings. They're about the size of a tiger and hunt in packs, and are shown to be some of the most intelligent dragons in the series. The species is first introduced when a couple of Dragon Hunters encounter one that's apparently injured, and are killed off-screen by the rest of the pack when they attempt to capture it. Later, Hiccup encounters the same Shadow Wing and narrowly escapes the same fate, only to find out that the "injured" dragon is just bait and is perfectly capable of attacking him itself.
- Even worse is the Shadow Wings' "boss", which is basically a giant mouth with wings wide enough to carry the entire Shadow Wing pack. When the smaller dragons join forces with the big one, they grab hold of its wings and basically act as living machine guns.
- The Shellfire. It more or less resembles a giant manta ray with horns and armor plating, and it shoots giant meteor-like balls of fire from a range of up to a mile. The fact that one of them is temporarily weaponized by the Dragon Hunters does not help.
- In Loyal Order of Ingerman after Fishlegs finds out his ancestors nearly hunted a species of dragons to extinction he has an unbelievably upsetting and frightening dream where he, acting completely out of character, hunts down his beloved dragon Meatlug. After cornering it with a disturbing Slasher Smile Fishlegs whips out a battle ax with an ax head nearly half of Fishleg's size (Fishleg's being one of the largest kid human characters) and looks about ready to embed the thing in Meatlug's skull. Fishlegs wakes up screaming and in tears.
- Season 7's new Big Bad Krogan gets an Establishing Character Moment both off- and onscreen to show he's a Knight of Cerebus beyond anything seen on the show before. Offscreen, Hiccup and Astrid discover Garff after a fight with him, covered in slash wounds that come close to killing him. Onscreen, one of his men has second thoughts about how brutal his methods are, resulting in Krogan making a show of letting him go, only to throw an ax right into his head.
- Episode 'A Matter of Perspective' from the same season is full of this. First, it takes place in Vaneheim, a final resting place of dragons. The scariest are however the Sentinels, the dragons that protect the island who have powerful air- blast based breath and remember most of strategies employed by dragons. They look like a statues while not active, but if someone tries to leave the island they instantly come to life, which is especially unsettling due to erratic movement they have during that phase.
- The Season 7 has also Viggo's new look.
- Slitherwings are entirely coated in poisonous venom that kills within a month just from touching it. If someone is affected, their only hope is an antidote that requires more of the venom to make, which is naturally very hard to get. And the fact they look like giant snakes does not help.
- The reveal at the end of Season 7 that throughout the entire run of the show, Trader Johann has been playing everyone by pretending to be a Lovable Coward with a bunch of tall tales, when he's actually a cunning and highly manipulative Dragon Hunter completely obsessed with obtaining the Dragon Eye lens in Heather's possession. And in the same scene as the reveal, he gets it, with our having no idea what this means, but it has to be pretty bad if he was willing to play this scheme out for years.
- And in Season 8 we get to see how disturbingly vicious and unhinged Johann can get. Hes not as physically powerful as Ryker or Krogan, but hes willing to stoop incredibly low and use violent, underhanded tactics just to get rich. He also mentions that the stories he tells were stolen from real merchants, whom he murdered.
- In the series finale, he tries to stab Hiccup in the face (possibly in the eye) with a dagger.
- Johann's death: He was frozen by the Berserker Bewilderbeast and slowly suffocated in the ice.
- In "Triple Cross", Viggo makes a HeelFace Turn. When he saves his Skrill, he gets shot with four arrows. He then sacrifices himself, and we never find out exactly how he died. This mixes with Tear Jerker and Awesome.
- Also, just how angry Johann gets when Viggo makes his HeelFace Turn.(Johann pins Viggo against the wall and holds a knife to his neck)Johann: You thought I wouldn't figure you out? I can smell betrayal coming from a mile away. I didn't spend years sniveling at the feet of every Viking in the Archipelago to be destroyed by some two-bit crime lord!
- And then he looks and sounds even more terrifying after Viggo uses Zippleback Gas from his sword to make an explosion and escapes.Johann: Get me Grimborn!
- Also, just how angry Johann gets when Viggo makes his HeelFace Turn.
- In the series finale, who should make a cameo but the madman himself, Drago Bludvist. Seeing Krogan, himself a formidable opponent, reduced to a cowering wreck before his boss really hammers home how utterly terrifying Drago can be. Drago then proceeds to sentence Krogan to death while chuckling. Drago: Ill find another King of Dragons myself...
- What makes it worse is if you listen closely Krogan is dragged offscreen, then seconds later we hear a loud SNAP followed by the sound of something heavy hitting the ground. Krogan is still begging for mercy right up until the snap...
Nightmare Fuel / Dragons: Riders of Berk