History Fridge / HowToTrainYourDragonTheHiddenWorld

*** And not drugging her ''before'' he allows her to "escape" ensure she can't warn New Berk about his use of such tranquilizers. The Berkians' skills at dragon-derived forms of chemistry are well known, Hiccup and Fishlegs could potentially come up with a counteragent if forewarned.

** Actually, it was never Stoick's plan to KillEmAll. Quoting from the first movie: "If we find the nest and destroy it, the dragons will leave. They'll find another home!" He likely was more ambitious in the past and hoped to stop humans and dragons fighting permanently, but later switched to simply wanting the dragons off of Berk after years of endless conflict left him much more jaded.

* The Hidden World, although revealed in "WesternAnimation/DragonsTheNineRealms" to have multiple distinct areas, would not be able to sustain every single Dragon species equally. Toothless and Hiccup deciding to move Dragonkind fully into the Hidden World may end up resulting in dragon populations having a lower quality of life, their numbers decreasing even more, or going extinct altogether, the opposite of their intended goal of protection.
** Tunneling species like Whispering Deaths and Screaming Deaths would not be able to tunnel without the risks of caverns caving in. Eruptodons may face a similar issue trying to find lava to feed on.

* The Hidden World, although revealed in the future sequel series to have multiple distinct areas, would not be able to sustain every single Dragon species equally. Toothless and Hiccup deciding to move Dragonkind fully into the Hidden World may end up resulting in dragon populations having a lower quality of life, their numbers decreasing even more, or going extinct altogether, the opposite of their intended goal of protection.

** Species that live in specialised habitats such as Snow Wraiths or Sandbusters would be more limited in where they inhabit than other dragons.

** Changewings and Scauldrons are also known to be predators of other dragons, perhaps with ample food in the Hidden World, as well as being under Toothless' command, they no longer have to eat other dragons to survive?

* [[spoiler: It's confirmed that the Dragons are hiding and waiting for the day when they and humanity can coexist. Now if history went the exact course to the modern era, that means]] [[spoiler: later sightings of mythical beasts and cryptids such as the Loch Ness Monster, the Thunderbird, Mothman, Yeti/Bigfoot and UFOs might have been actually the Dragons coming out of the Hidden World to confirm if humanity is ready for them]].

* [[spoiler: It's confirmed that the Dragons are hiding and waiting for the day when they and humanity can coexist. Now if history went the exact course to the modern era, that means]] [[spoiler: later sightings of mythical beasts and cryptids such as the Loch Ness Monster, the Thunderbird, Mothman and Yeti/Bigfoot might have been actually the Dragons coming out of the Hidden World to confirm if humanity is ready for them]].

* [[spoiler: It's confirmed that the Dragons are hiding and waiting for the day when they and humanity can coexist. Now if history went the exact course to the modern era, that means]] [[spoiler: later sightings of mythical beasts and cryptids such as the Loch Ness Monster, the Thunderbird and Yeti might have been actually the Dragons coming out of the Hidden World to confirm if humanity is ready for them]].

** A Speed Stinger pack from the tv series developed webbing feet to run on water in “The Next Big Sting” and the Cavern Crasher was able to swim from long distance from Fireworm Island to a Singetail Islam’s in “Family Matters”,

* Grimmel mentions that Night Furies are particularly susceptible to cold temperatures. Remember when Valka first encountered Hiccup, and Toothless fell into the icy water where the Seashockers carried him to the dragon's nest? How close did Toothless come to succumbing to the cold?

** The Sentinels are left with an uncertain situation. Vanaheim is their home and they might have either fight to the end or had to abandon the island. Or they might remain there for another decade or so, then realize that there aren't any more dying dragons coming to Vanaheim's "dragon graveyard" and accept that they are free to cease protecting it and migrate to the Hidden World as well. And worse, this would made the dragons' departure all the more depressing as the Dragon Riders knew some of those dragons like Thornado, Torch, Garff, the Fireworm Queen, Scauldy, Smidvarg and Darkvarg.

** It's likely the four individuals enslaved by Grimmel were killed by Toothless' lightning shock.

* One might wonder just how come Hiccup was unharmed when Toothless fried the Deathgrippers. Well, Toothless is shown to also be lightning-proof - or rather, he's basically a Faraday cage - it goes around him and not in him. Hiccup is wearing a suit made from shed scales, so he's also in a faraday cage. Thus the electricity went to the next least-resistant thing - the other dragons holding onto them.
** Either that, or electricity simply doesn't do any damage or harm to those scales. They may be designed to channel the electricity. Either way though, it's essentially a RequiredSecondaryPower of Toothless's "cloaking" ability.
** Furthermore: why does Toothless, a Night Fury, need extremely hot lightning to become invisible when his lighter-coloured counterpart only needs a plasma blast? Potentially due to his increased pigmentation.

* WordOfGod claims that the Light Fury is a different, related species, which begs the question on whether they can successfully cross-breed with Night Furies. If yes, then there is at least some hope for the Night Fury bloodline, even if they are no longer pure-breds, but if not, then Toothless's kind truly is gone for good...
** Even if they are able to cross breed, it won't save the species, as the Night Fury will eventually be bred out of their descendants. And there is a chance, like with some hybrid crossbreeds (Mules) that their offspring might be sterile and unable to reproduce at all.

** They are still mostly one color or the other, [[JustifiedTrope plus they are now living in a world where day and night are largely meaningless]].

** Which is why it's good New Berk is able to check up on them, and Toothless' family trust the humans enough to take Toothless to them for repairs to the fin if need be.
** In the epilogue, Hiccup asks about the fin and mentions some tune-ups he has in mind.

** The Wing Maidens would be equally devastated in letting go their Razorwhip charges.
*** This becomes FridgeHorror when you remember the reason why the Wing Maidens care for the Razorwhips (The Males kill the Children and the Females are too weak to put up a fight); this could ultimately lead to their extinction unless there are Dragons in the Hidden World that naturally do what the Maidens do (and since they claimed that the Razorwhip Species was almost driven to extinction, there probably aren't).
*** As long as Toothless is around, the Males would never have the chance. But after he dies, that's another story unless the role of Alpha is passed on to Toothless's Night Light kin.
*** Alternately, the baby Razorwhips might be entrusted to ''other dragon types'' to rear until they're capable of avoiding the adult males' predatory impulses. There are a ''lot'' more dragon species in the Hidden World to choose from, to foster their hatchlings off to, than there ever were on Wingmaiden Island.

** The Sentinels are left with an uncertain situation. Vanaheim is their home and they might have either fight to the end or had to abandon the island.
*** Or they might remain there for another decade or so, then realize that there aren't any more dying dragons coming to Vanaheim's "dragon graveyard" and accept that they are free to cease protecting it and migrate to the Hidden World as well.
** And worse, this would made the dragons' departure all the more depressing as the Dragon Riders knew some of those dragons like Thornado, Torch, Garff, the Fireworm Queen, Scauldy, Smidvarg and Darkvarg.

* Aside from explaining why the modern world isn't full of dragons, the ending also explains why Hiccup's inventive genius didn't ''bring about'' the modern world, several centuries early. Over the course of the films and series, we see him perfect his various devices, from weaponry to flight equipment to apparatus for the village ... but we ''also'' see those inventions become progressively more dependent upon dragon byproducts: Gronkle iron, Monstrous Nightmare gel, shed scales, etc. When the source of these materials departed forever, Hiccup would've had to start over from scratch to re-create such mechanisms using mundane resources: a task that would've been grueling (because he's not inventing fun ''new'' stuff, just slogging away at boring old stuff) and probably impossible in many cases. Between his duties as Chief and his responsibilities as a husband and father, he never really had the chance to pursue his craftsmanship in depth, after the dragons left. And when he ''did'' try, he'd constantly be reminded of "If only Meatlug was here to refine this ore..." or "I used the same kind of buckles on Toothless's saddle-cinch ... gosh, I miss flying with him...". So, his inventions became more of an occasional hobby than an obsession, and in the years to follow his death, his existing creations broke down one by one and were never replaced.