The Forbidden Friendship scene where Hiccup tries to approach Toothless close up. When Toothless sees him drawing a picture of himself, the dragon tries to draw his own version on the ground around him, to a light twinkling melody on the soundtrack. When Hiccup learns that he must not step on the lines of Toothless' drawing, he effectively goes into a dance avoiding them, climaxing when he is face to face with the dragon. At that moment, Hiccup takes a leap of faith, averts his eyes and reaches out for the dragon; when Toothless touches him in response, it is an act of trust that will begin to change everything about both their worlds.
The little uncertain false start that Toothless gets sells it.
Astrid's first flight with Toothless, in which she goes from hardened warrior to awestruck teenage girl (and no, in this case that's not a bad thing). Especially the moment when she unselfconsciously wraps her arms around Hiccup and leans her chin on his shoulder - judging from the look on Hiccup's face, that's just as amazing as the flying itself.
Astrid's little talk on the top of the wharf after the vikings left for killing all the dragons
The ending where Toothless helps Hiccup walk with his new artificial leg. Also the five minutes preceding that scene where Toothless has Hiccup covered in his wings to shield him from the explosion. Warning: these scenes mayreduce you to tears.
If not then the music that plays during the scene when Hiccup realizes he's missing his leg will.
Toothless' tail sweeps into frame as he helps Hiccup to the door, and you realize that their bond will be stronger than ever before since the boy & his dragon have another thing in common.
"I'm proud to call you my son." There's a moment in a parent's life where you suddenly look at your child and think, "Wait a minute, when did you become this person?" and it's usually when they're around Hiccup's age. He's spent his whole life being a disappointment to the village because he can't be what the rest of them are, so that's really all they know of him but when the Green Death is laying waste to all of the vikings and their ship, and Stoick is prepared to die just for a slight advantage, the children come flying in on dragons, overturning generations of belief. All the time Hiccup has spent working with Toothless is reflected in this moment, when he and his peers and doing something no one else ever dreamed of. When Stoick says he's proud of his son, it isn't because Hiccup has met the standards that everyone else has already set. It's because he's done something amazing, on his own, and developed into a strong and independent person that his father didn't even realize was there. It's truly an emotional moment in any parent's life.
A close second to this one - the scene as the kids arrive on the dragons, Gobber turns to Stoick and points out that Hiccup is just as stubborn a viking as Stoick ever was. The look on Stoick's face as he nods in response to this comment is a testimony to the CGI artists' skill.
After Toothless refused to share his food with the Terrible Terror, Hiccup did. The tiny dragon then cautiously approached him, then curled up and fell asleep under his hand.
The scene where Toothless finally lets Hiccup touch him.
What makes the drawing part even more heart-warming...Toothless gets "inspired" to draw something after watching Hiccup do a sketch of him in the dirt. As he draws, he looks back at Hiccup for a moment before returning to the drawing. And then the Late to the Punchline moment passes and one realizes he was trying to draw Hiccup. Furthermore, after Hiccup gets the idea that he mustn't step on the lines, he effectively goes into a dance stepping around them, with the score playing "Forbidden Friendship" until he winds up in front of Toothless and then he takes the above leap of faith.
EVERY scene with Toothless. He's like a big kitty in dragon form.
When Astrid punches Hiccup ("That's for kidnapping me!") and then gives him the most adorable shy-girl kiss on the cheek ("That's for everything else.").
And then at the end of the movie... After Hiccup walks outside, seeing the Vikings and dragons getting along peacefully and working together, Astrid punches his arm again, saying "That's for scaring me! (in reference to his Disney Death). Then when he protests, she kisses him right on the lips. The rest of the line goes unspoken, but is heavily implied.
Necessarily brief, as it occurred during the Final Battle: when Toothless snatches Astrid out of mid-air, he looks around to make sure she's all right. She smiles back, and his eyes dilate and he makes his "happy to see you!" warble. He likes her!
A heartwarming moment in very tense and terrifying scene: Toothless stopping immediately from blasting Stoick in the ring when Hiccup screamed at him to stop. The absolute trust he has in Hiccup, so much so that he stopped the attack completely is beautiful, and made his subsequent capture even more gut-wrenching.
The part after the Green Death is destroyed when Stoick is searching frantically for his son. Toothless (who has Hiccup perfectly safe in his wings) is lying down nearby, and that measured look of cold disapproval he gives Stoick as he mourns the apparent death of his son shows that he'll only allow Stoick near after he's realized his mistake. It makes you realize that he's looking out for his friend, to the very end.
Toothless didn't just become my friend. He became the friend who gave me my purpose.
The scene where Astrid encounters Toothless for the first time. She has just been yelling at Hiccup and beating him up for suddenly being so good in dragon training, but when she sees Toothless her first instinct is to push him to the ground and try to protect him from a perceived threat, showing how she's not so bad after all.
Also, how Toothless and Astrid are both trying to protect Hiccup from each other.
After Stoick saves Hiccup from drowning, he immediately dives back in to get Toothless, having accepted that his view of dragons is wrong. Once he breaks Toothless free from his bindings, Toothless carries him to shore.
It's brief, and not as strong as the other examples listed here, but Ruffnut being able to pull Tuffnut out of a Nadder's fire when they were arguing literally a second before. Later, as soon as she senses trouble, goes to check if he's OK during the Zippleback exercise without a moment's hesitation. As much as they argue like brats, it's nice to know at least one of them's looking out for the other.
Stoick: I can buy the men a few minutes if I give that thing something to hunt.
Gobber: *clasps hands with him* Then I can double that time.
After getting back from the dragon's den, Hiccup begs Astrid not to tell Stoick about it because he's afraid his father will kill Toothless. Astrid asks if his "pet dragon" is more important than the island they've been looking for for centuries, and Hiccup simply says yes. What's heartwarming is that Astrid immediately backs down and agrees to give him time to figure out what to do, showing how much she's grown to trust him just from her brief experience with him and Toothless.
The part at the very end with the perfect capper to the "All of...this" Running Gag. After the gag was used to signify that Hiccup had to stop being Hiccup in order to be a true Viking, Stoick instead pats his son on the back and says "Turns out what we needed was a little more of...this!" The way Hiccup then says "You just gestured to all of me" followed by Stoick's very lovely smile perfects the scene.
Gobber's relationship to Hiccup is one of the best Parental SubstituteVitriolic Best Buds relationships ever! In spite of all of Gobber's gentle ribbing, he's extremely protective of Hiccup and is one of the few Vikings pre-Toothless who saw more in Hiccup than just a scrawny nuisance.
As funny as the "breast-hat" scene is in its awkwardness, the fact that Stoick wears part of his departed wife's armor on a daily basis because it "Keeps her close" is quite sweet in its own way.
Stoick and Hiccup's "Brest-hats". Yes the helmets made from his mom's brestplate was played for laughs, but Stoick's genuin, "keeps her close." comment rings true. In the post movie works Hiccup is seen wearing it proudly.
Gift of the Night Fury
Just about the entire "Gift of the Night Fury" short, but especially the titular gift. After being given an interlocked tailfin so he can fly independently, Toothless uses it to retrieve Hiccup's helmet, returns, and then systematically destroys it, insisting on the old saddle and tailfin - and his bond - instead.
The scene at the begining of "Gift of the Night Fury" when a small chlid (wearing a dragon costume no less) growls at Fishlegs' Dragon, the Dragon responds with a small growl of it's own. What does the girl do? She giggles!
The Book of Dragons
In "The Book of Dragons," it's of course Hiccup who gives the lesson on Night Furies. When talking about Toothless, he comes to this touching line:
Hiccup: I have so many questions about him, but there's one thing I do know.
Literature: How to Train Your Dragon
The relationship between Hiccup and Fishlegs. This comes to a head in How to Cheat a Dragon's Curse when Hiccup goes on a dangerous quest through enemy territory to get an antidote to save his friend's life. The ending makes it even more heartwarming — Hiccup actually got bitten by the Venomous Vorpent. He spends the whole book dying, and he doesn't even realize because he's too busy trying to save Fishlegs.
How to Train Your Dragon 2
In the trailer:
Astrid: What you are looking for is right here. (Laying her hand on his chest)
Toothless and Hiccup play-fighting. Nothing looks and feels more adorable than seeing it and it goes to show just how much their friendship has grown since they first met!
Complete with Forbidden Friendship playing in the background.
Hiccup: Should I know you?
Valka: N-no... You were only a babe. But a mother never forgets.