Short version: HTTYD: The Hidden World has numerous plot holes, uses ex-machina plot devices, introduced an incompetent villain who succeeds through chance, completely changed the characterization of key people compared to the prior films, ignored existing foreshadowing, misunderstands the concepts of maturity, leadership, and friendship, applauds toxic relationships, proposes race-segregation and isolation as the means to peace between different groups, turned Hiccup into the instrument of Grimmel's lasting victory, and proposes that social change can happen without anyone actively working for it. In other words, we can give up on our dreams for a better world and maybe the world will change for the better. For these reasons, this film is a narrative disaster and is completely unbecoming of the franchise.
Long version: Where to begin? What is the question that the final film and the entire series of three films has been asking?
The question that overarches the entire movie series is that of the relationship between humans and dragons. It all began that moment in the cove when Hiccup stopped trying to control the situation, extended his hand to Toothless, and let the dragon choose whether to trust and take a risk. Is it possible to have true peace and friendship between these two groups of different types of life, of people I would say? Is it worth inviting someone very different from oneself into ones life and world to try to live in peace, even if the transition is rocky and uncertain for both sides involved?
Other questions, such as 'Will Hiccup get a girlfriend/get married?' 'Can Hiccup make his father proud/be a competent Chief on his own power without a dragon to aid him?' 'Will Toothless find a mate?', while a key part of the journey, are purely secondary to this most fundamental question that is asked for the first time in the cove and underlies each of the three films.
Establish something, test it, and then reject or reaffirm it. This is the three step process for establishing a resolution to a mission or purpose. The establishment of that dream/better future happens in that moment in the cove. You and me are very different life, but maybe everything we thought we knew about each other is wrong. We can fly the winds of life together. This is something that must happen outside civilization or stifling custom and expectations. That makes Hiccup perhaps the only person who could do it initially because of how thoroughly he did not fit in and already felt like an outcast. What is the testing of the dream? Obvious examples are Drago Bludvist, who seeks 'peace' through control and subjugation instead of loyalty and friendship, and almost all the early events in film III pertaining to the armies who threaten and lay siege to Berk under Grimmel's archetypal intolerance of 'us or them'. What are the lessons from these incidents? Some humans are bad. Some dragons have the potential to be bad. Dragons must be respected in order to 'earn their loyalty,' just as humans must be.
But the forces of intolerance, old prejudices, and fear are very strong. The world in the above is too violent for dragons in general. All on Berk, dragon and human, are not safe anymore and must disappear completely off the map. The obvious question follows then – what is to happen to the relationship between these dragons on Berk and the humans on Berk? We know where the dragons must end up in hiding but should these specific humans be allowed into the hidden world to live in peace with their dragons? Is that even possible?
The humans of Berk make it clear what they are willing to do when they leave Berk behind and set out in search of the hidden world. They are willing to leave behind their old identity, to stop being Vikings, so that they can remain dragon riders and be loyal to the different part of their family. They are willing to become refugees and immigrants after years of fighting on behalf of dragons' freedom and suffering as a result. Everything that happens from that moment they started fighting the trappers and dragon hunters is another type of extending the hand of trust to dragons in general. I would conclude that these humans have done their part, and their dragons should know this. This is a powerful message and an obvious setup for something else.
On this point, we must ask ourselves the following question. What are the dragons? Are they pets or something more? The film portrayals appear a bit conflicted on this point. Plenty of actions speak of higher intelligence, reasoning, foresight, and a system of right and wrong. Some examples from the films and from the expanded universe, for those willing to look to those episodes, being Toothless understanding spoken words and even miming speech in his film II 'big baby boo' moment, Toothless getting out of various traps, planning to trick the Outcast guards, his careful and deliberate actions when playing with Hiccup in film II (by the way, this type of physical play is something very fraternal and definitely not something that suggests a master-pet relationship), his trust given to Hiccup in the cove only after Hiccup fully trusted him by looking away, his protectiveness and care for Hiccup in film I, and his film I returning the favor of sparing Hiccup's life and giving him a fish gift. The most glaring examples however, are when Toothless refuses to kill Hiccup in the woods, something that a truly wild and natural predator would have done, when Toothless draws the Light Fury in the sand, which shows a very advanced imagination and ability to personify the 'other', and when Toothless breaks free of the Bewilderbeast control and defies the 'natural way' of submission to the Alpha. In those moments, Toothless takes a step back from nature and says 'No, I will not submit. I want to change the world.' He is free in that action. To me, these portrayals equate to dragons being people with the same 'spark' and 'free will' as humans, even if the dragons do not build things like humans do, lack an audible or written language, and have generally simpler lives with less complex motivations.
On the other hand, the writers included odd and contradictory scenes, such as the prosthetic chewtoy scene in film III (which directly conflicts with the brotherly play in film II), Hiccup's possibly sarcastic but still belittling reference to dragons being 'pets' at the end of film I, the inclusion of 'buttons' that someone could push, such as chin scratching, to get a reaction out of dragons, and some other scenes in the wider series in which Hiccup/other teens do things that treat dragons as tools to use.
There seems to be far more compelling evidence of in favor of dragons being 'higher animals' than there is against, but there are some conflicting messages sent here.
Back to the initial question of the film's resolution. Physical ability for humans to live in the hidden world is not an issue given that we know Valka lived with the Bewilderbeast for twenty years and humans are the most adaptable animals on the planet. The presented obstacle though is what we saw as the natural reaction of free dragons, as the writers portrayed them, in the hidden world to the presence of humans. Specifically, the reaction of open hostility to the two humans that they do see, Hiccup and Astrid. Wariness would be understandable. Open violence is not. For one, animals that do not know humans do not know to fear humans because they have no history of being hunted. Secondly, the dragons' reactions in Gift Of The Night Fury when Hiccup is on their egg-hatching island are very calm and nonchalant. Even if these are dragons that do know humans, there should be nowhere and no situation which would make them more wary than for a human to be around their eggs and offspring. The hostile reaction of the hidden world dragons does not make sense unless the writers were trying to force one specific outcome. It also has significant consequences for those who consider the film's ending bittersweet with hope that the dragons will come back one day as Hiccup suggests. This will be explained a bit later.
So now we have established that the hidden world is 'not a place for humans'. That means that the final battle against Grimmel in which Toothless almost dies and has to be rescued by a fellow dragon instead of a human like how Hiccup saved him from a fall in film II shows Hiccup and Toothless that lasting peace between their kinds is not possible in the world above. There is too much danger. Humans cannot be safely brought into the hidden world. There is too much danger. We have now forced the separation of these dragons from their humans, as happens at the end of the film. This is one way to lead into those fateful words 'There were dragons when I was a boy.'
This is where the writers completely got it wrong and even missed foreshadowing embedded in the first two films. Consider the following points.
One, Hiccup leaves the village, goes out into the wild, enters a little hidden world (the cove), meets a wild dragon, disarms himself through an act of trust, and interacts peacefully. The dragon is initially suspicious, not violent, and learns that it can trust this very different creature. This works on the level of the individual. Can it work on the level of entire tribes? I would argue that the Berk humans' actions throughout are an extension of a hand of trust to all dragonkind. The parallel was perfectly set up for a larger scale replication of this most powerful moment in all three films. This moment that 'changed the world forever'.
Two, the Berk humans invited dragons onto Berk after the Red Death's downfall. Was that an easy transition? Definitely not, as those who followed any of the expanded series knows. Mildew and company are perfect examples of the counter to this change. But the dragons trusted that the humans would not hurt them and 'moved in'. Why did it work? It worked because Berk had a strong Chief/Alpha, Stoick, who worked to keep the peace and gave the dragons a chance. It worked because the humans who were friendly to dragons actively defended their friends from other humans who would do the dragons harm. It worked because all who stayed on Berk gradually came to trust the other side through long exposure. Wariness is a normal, even prudent reaction to something new and unknown. Open violence and hostility is not a given. There is no reason to assume that Toothless as King of the hidden world would not be able to enforce and keep the peace as Stoick did on Berk. There is no reason to think that the bonded dragons would not defend their humans against aggressive dragons, just as the humans did against their own violent members. There is no reason to assume that the dragons in the hidden world will not become gradually more accepting of these humans through long, peaceful exposure, just as the humans of Berk did.
Finally on this point, consider that the life of a dragon rider is hardly 'safe'. Seeing a few dragons get snappy at them is not a new occurrence and should not be a reason to give up hope. Any remaining danger is just 'occupational hazard' which I suspect these riders would gladly have embraced.
Three, Valka's presence in the wild nest for over twenty years is an obvious foreshadowing of it being possible to live in harmony with wild dragons. Surely the Bewilderbeast King helped in that regard.
Four, Valka's words to the heartbroken Hiccup after Stoick's death in film II are blatantly clear foreshadowing – 'Only you can bring our worlds together. That is who you are...' The unspoken corollary is that if he cannot do it, no one will.
Five, the Berk humans leaving Berk and becoming a refugee people is a clear and definitive statement that they are not Vikings anymore. They sailed to Berk and flew away from it. They have become something different and, if presented with a return to what they were in the past, symbolized by Berk as the home of their grandparents, they would choose to leave behind that past. They would rather become immigrants than break up their extended family. That is a powerful message and is a perfect example of a 'letting go' and 'moving on' that is uplifting and good to teach.
Further, even if the Vikings have become comfortable on 'New Berk' and want to settle down now, they cannot remain there after the events of the film. It should be clear why. New Berk is on the map now. The armada found them. Any survivors on the ships will know that the people on New Berk know where dragons must be in hiding. The Berk people must leave again anyway.
That moment in the cove between two people was a two-way choice. Trust must be offered and given on both sides. Here is where the film completely breaks down, at least to me.
What is the decision of the dragons once it become clear that they must leave, and in what way does that decision reflect a judgment on their humans? The dragons, Toothless included, who have lived with their humans for seven years will not make an exception for these humans who have done everything possible to prove themselves. The dragons do not choose to protect their humans as the humans did for them back on Berk. The dragons choose to 'fly on their own' and be free of all humans.
I think that the writers tried to counter Grimmel's intolerance by having the Light Fury catch Hiccup in that dramatic scene near the end. This was an attempt to prove Grimmel wrong in that the Light Fury judged this human worth saving even after all the fear and hostility she showed to him in the past. How easily could that have led directly into them all leaving together? But alas, the dragons prove Grimmel correct when they choose to 'fly on their own' and embrace isolation. More on that later.
What is the commentary that this resolution makes on certain important issues facing the world today? I submit to you that there are two hidden messages buried under the surface themes of 'letting go', 'moving on', 'maturing', and 'flying on your own.'
One message embedded in this film is that the way to ensure peace among different groups is to physically segregate them by race – the human race and the dragon race – with no exceptions. This is morally repugnant to propose as the answer. Peace is only attainable through living together in a joining of lives in a way for better or for worse. Yes, there are 'occupational hazards' in making such a world. Some feelings get hurt, and some people might not like it at first. However, that melting pot of cultures is the only way to bring about change. Anyone who watched the expanded series knows that it was not easy for Berk after inviting dragons onto the island following the events of film I, but it was still definitively worthwhile. Replace the dragons and humans in this film with any two human ethnic groups that have been in tension and it is clear how vile that separation conclusion actually is. And remember, we established above that these dragons are not simple beasts, mounts, or pets. Rather, they are people.
Another related message is an explicit commentary on the nature of immigration. The refugees from Berk seem willing to immigrate to the hidden world at first and are unable to remain on New Berk even if they might like that place at first. However, the free dragons, the existing denizens of the hidden world, are violent and hostile to the humans who would want to live in peace with them. This is clearly a deliberate decision by the writers to reject the possibility of immigration, to portray the dragons as isolationist with no exceptions, and to throw up a wall, so to speak. This is also heinous to propose. Further, it is in contrast to what we saw the Berk humans do in film I when they invited dragons onto Berk to live in peace. That is a beautiful parallelism that was obvious.
But the writers chose not to do that. Why? This was possibly done under the reasoning that humans would pollute or corrupt the hidden world in time. But what is that corruption that would happen? The Light Fury appears to display this very fear or concern, given how she was muzzled and used as a tool by Grimmel. She wants dragons to be free, to not be slaves. She sees Hiccup frequently riding on Toothless and thinks that this is another type of control. What could Hiccup possibly do to convince her that dragons are not pets, mounts, or slaves to the Berk humans? The only possible thing is to repeatedly fight for dragons' freedom, free them from traps, give Toothless his freedom, and be willing to let him go. That moment must happen and does happen high in the sky when Hiccup tells her to 'Save him!' Hiccup and the entire tribe cannot force dragons to accept them. They can only extend the hand of trust, turn away, and let the dragons choose based on what they know of these humans. There is an obvious character arc for the Light Fury here, all of which culminates in that moment when Hiccup embraces Toothless and lets him choose. That moment is conclusive proof that dragons are not slaves or trapped by these humans. But the writers were apparently blind to that obvious character arc.
I have a response to the critics, many viewers, and even the directors who will say that this film is about maturing, letting go, growing up, and that the series was given a 'bittersweet' ending. First, the points about coming into ones own as a capable leader, gaining confidence in oneself, letting go control in favor of trust, and growing up are all necessary and good points. Hiccup does need to learn that he can make decisions and have 'presence' as a leader without having a dragon there to enforce his actions. I quite like the idea that Hiccup starts out this film overly reliant on Toothless because of buried grief from losing his dad. That is character flaw which then allows for growth throughout the film. Toothless does need to accept the automatic tailfin so that he can 'fly on his own'. However, all these good points about competency and leadership can be developed independent of a thoroughly tragic ending.
For that is what this ending is, a complete tragedy covered over with empty words of hope and an ending scene of 'cuteness' to distract the viewer. It is not bittersweet. Bitter it certainly is, but the 'sweetness' is empty if we stop and think about it. Why?
After the departure of the dragons and toward the end of the film, Hiccup infers that the dragons will come back when the world is safe for them. Remember though that the established 'natural state' for the dragons in the hidden world is aggression and violence toward humans. Hiccup's story of what dragons actually are might take hundreds of years to affect change in the world, if the story is told at all. Changing traditions and cultural mythologies takes a very long time. Let us assume though that the world above is eventually made 'safe' for dragons again. By that time, there will not be any living dragons that remember humans as trustworthy creatures. They will only have their 'natural instincts' which we saw in the hidden world. So to those who would hold onto that 'they will come back when the world is safe' idea as a 'bittersweet' resolution and a looking to the future, I have one question.
They will have no reason to ever fly into the above again. There is no one to tell them that is it safe for them again. They remember no one up there worth seeing. That makes Hiccup telling his story to the world completely irrelevant. It would almost be better to not tell that story and hope that dragons completely fade from all recollection so that they can live in 'freedom'. The ending scene of Toothless and the Light Fury showing off their babies is not bittersweet at all because it does nothing but tear open old scars and remind Hiccup and family of what will not be. A brief meeting, flight, and showing off of the Night-Lights to Hiccup changes nothing. It is also telling that Toothless does not initially recognize Hiccup upon that meeting. He does not know this human whom he spent almost seven years alongside. It is also another contradictory portrayal because the Night-Lights should be hostile and suspicious of these humans, if that is truly the 'natural condition' and 'destiny of the dragons'. Both Hiccup's words to the fallen tribe and the ending scene with the cute Night-Lights are hollow without consistency or substance behind them. The writers hope that viewers will not question his words and will instead take them at face-value.
Another way to think about this is to ask what if someone found that hidden world today and went down into it? Why is there any reason to think that the dragons within will be peaceful and will not react with the same hostility that Hiccup and Astrid once encountered. Long isolationism and segregation has never been an effective way of promoting peaceful interactions once individuals try to cross borders. Therefore, the film ends in much the same place that was before film I – humans and dragons unable to interact peacefully, only this time they will not see each other at all. There is no reason to think that there will ever be peace again. Hiccup's story changed nothing about the world. After all, wild beasts do not belong in the human world, as seems to be a message of this film.
This film also fails to display any true maturity in Hiccup's decision-making or capacity as a leader. He gives up in film I after his failure to convince his tribe, and Astrid had to talk some sense into him and motivate him with her 'So what are you going to do about it' speech. He gives up in film II after his actions cause his father's death and Toothless's enslavement. Valka had to talk some sense into him and motivate him with her speech about how Stoick never gave up on him and Hiccup has a great destiny to effectively change the world. He gives up in film III after the battle is apparently won and the villain defeated. There was no one there to talk some sense into him or motivate him to not give up hope.
Further, Hiccup's approach to making decisions is not mature or what would be expected from a competent leader. The departure from Berk, while a very symbolic moment, was essentially a unilateral decision. A leader will at least hear the thoughts of others on a matter as serious as relocating the entire tribe. This continuing flaw of his is most obvious though is his decision to tell Toothless to lead all the dragons away into hiding. That is also a choice that is not his alone to make. Hear from the tribe first since the dragons are part of the Berk family. Also, this decision of his was made hastily in a very emotional situation right after both he and Toothless almost died. It is not mature to make such life-changing choices in a highly emotional state.
Also, as I mentioned in the short version, Hiccup becomes the instrument of bringing about Grimmel's ultimate goal of seeing dragons gone from the world. Hiccup gives up on the idea that people can change, and he accepts Grimmel's core tenant of isolation and segregation of the races. I cannot understand what the directors were thinking when they decided to make this existential despair the culmination of Hiccup's character arc.
Even in addition to these more substantive objections raised above, there are other minor objections and points of inconsistency.
First, Toothless's artificial tailfin will eventually break. You do not get to sprinkle magic dust on something and make the problem go away. Every mechanical construction will rust or wear with enough use. There is no answer for this problem if Hiccup is not around to provide routine maintenance. This also has significant consequences for Toothless's future as an Alpha. Wolf packs and other animals that have hierarchies with an Alpha are good examples of what might happen. An Alpha that has a weakness or injury that prevents them from being able to protect the pack will be deposed by a more capable challenger. The consequences for Toothless are clear and not good.
Second, the lightning cloaking is too 'magical' and hard to accept as plausible without any forewarning. Toothless should already have known about that ability of his. Plus, being able to use it with Hiccup flying with him at the time is too hard to believe, especially with Hiccup's metallic prosthetic.
Third, using Deathgripper venom as a method of mind control against the Light Fury and even against the Deathgrippers themselves is an old idea, a rehashing of Bewilderbeast mind control. It also reinforces the naive idea that all dragons are merely innocent victims of humans, which is a theme that does seem prevalent through films II and III.
Fourth and as previously mentioned above, what happens with Grimmel's fleet after the dragons are freed from the cages and eventually fly off into the sunset? Does the fleet turn away and leave the Berk survivors on that island to live forever in peace? That does not sound plausible. Their entire livelihood depends on them finding where the dragons are in hiding. Rather, they would land on the island and take it by force or they would spread the word about where that island is. New Berk is on the map now, which means that it does not matter if the Hooligans like where they are and would prefer to stay put.
Fifth is a subtle observation based on musical motifs. The crescendo played during Toothless's departure is the same motif that plays during Valka's past abduction and Toothless's breaking free of the Bewilderbeast in film II. Both are moments of 'freedom'. Valka becomes free of Berk, and Toothless becomes free of the Bewilderbeast. The implication is that Toothless must and should become free of Hiccup because Hiccup is somehow keeping him a slave.
Sixth, the relationships of the other dragon riders to their dragons are quite ignored in the callousness of the departure. The other riders are basically just plot devices. Snotlout's pursuit of Valka was confusing and disturbing. Cloudjumper and Valka seem to part far too easily for having spent decades together. The dragons were portrayed as though the past seven, or far more, years did not matter at all to them, which directly contradicts the 'This is what it is to earn a dragon's loyalty' moment in film II. Further, the riders flying to the dragons' rescue and releasing them from the traps is a perfect example of 'This is what it is to earn a human's loyalty', another perfect but missed parallel and role-reversal. Friends who abandon their friends because of danger are faithless and traitors.
Seventh, that final meeting between Hiccup, Astrid, Toothless, Light Fury, and respective children is obviously a contrived meeting that breaks suspension of disbelief. All those dragons just happened to be flying in the above and coincidentally came upon the ship in the mist by the entrance to the hidden world? No. That would not happen. Further, and a very morbid point to mention, shouldn't Toothless have attacked the ship instead of landed on it? Toothless did not recognize anyone on this ship from afar. What if the ship was actually a ship of trappers? Dragons that fly outside the entrance to the hidden world are 'guards' after all. If 'The Alpha protects them all', then he should have attacked the ship and destroyed it, the same as we see happened to the ships in the fog on the journey to dragon island in film I, killing Hiccup and family in the process.
Eighth, the closing lyrics are almost insulting in how childishly naive they are. Specifically, the lyrics that 'We'll/Be Together/From Afar'. This passage is an obvious attempt to sugar-coat the ending. Not only that, but it is self-inconsistent and does not reflect how friendships truly work in real life. There must be shared activity and engagement with the other to be able to sustain a friendship. People change over the years and must stay in regular touch to keep a friendship alive.
I do not want to consider the events involving the dragons' departure and what follows to be canon. It feels like it was written by writers who turned a blind eye to the foreshadowing, themes, and progression in the first two films and who did not know what message they were trying to send. As should be clear from the above, the plot begs for and points toward one specific bittersweet yet hopeful resolution. I find it incredible, as in hard to believe, and heinous that the writers chose to establish absolute race-based segregation, isolationism, and rejection of immigration and refugees as the means to establishing and preserving peace between two peoples. Maybe they were unaware of this message, but I find that hard to believe.
The Berk humans leaving behind the world they knew and trusting in the dragons to lead them to peace and protect them in a new, strange world together would have hit all those themes of 'moving on', 'letting go the past', 'flying on your own', meaning competence and confidence in ones own leadership capacity, and trusting the other group while still ending up in the bittersweet resolution that must be. Specifically, that of dragons vanished off the map and eventually being relegated to stories and myths. However, this ending as I just described it keeps the bittersweet hope that maybe they will come back when the rest of the dragons have learned to trust the humans they know and when the above world is safe for dragons again. Both are necessary. Learning to trust humans can be done with the humans who deserve it and are in hiding with them. How can the world above be made safe for dragons again?
Hiccup will eventually leave the hidden world with Toothless and will live for a while as a wandering storyteller. He will tell the tribes this powerful story with the potential to 'change the world forever'. On the one hand, he knows that he failed and was not able to change the world in his own lifetime. The forces of hate, suspicion, and exclusion were too strong. On the other hand, there is still hope that maybe one day the dragons can come back to the above world. Maybe his own story can touch enough hearts and minds to change people over many generations. People above might change their stories about dragons and be more open to the new, even though he will not live to see that change happen.
Then, after the mission is finished, the two old friends and leaders for their kinds will fly back into hiding together where they see the world that they have built through the years. Dragons and the Berk humans living peacefully together, the dragons being totally free to come and go as they wish because they are not pets. This hidden world may never come forth because it is out of their control now. It depends on how the world above reacts to Hiccup's story and whether people can change. Toothless then flies off to another part of the hidden world to resume his Alpha-Kingly duties while Hiccup returns to being Chief. They are both competent leaders who are perfectly fine with some necessary separation because they know that they will see each other again before too long. Their relationship is changed because they have more duties that are not to each other, but they are still friends who regularly keep in touch. That is what best friends actually do in life. They are able to fly on their own, but they make sure that their flights cross paths.
That ending as I just described is the true, bittersweet ending that this series deserved.
I would also refer you to 'The Hidden World - Alternate Ending' written by 10Blue10 for additional film-related thoughts, many of which parallel mine but also consider additional reasons more focused on the theme of personal growth.