I think the last scene in Not Lout is maybe one of the best moments of character development in the entirety of the httyd franchise, fight me
Like, Snotlout from the very beginning is this kid whose been raised to be a fighter, to do whatever it takes to be at the top. He's rude and he's doing his best to be what he thinks is expected of him. And on some level he knows that he doesn't know what's expected anymore. The archipelago is no longer torn with dragon war, and where does Snotlout fit into Hiccup's world? Hiccup changed everything, and the place Snotlout was raised to take doesn't exist in the same way anymore.
All the while, his father makes it seem like he needs to be a winner in every competition, even when it isn't a competition. His father gives him generally horrible life advice, like rest is for the weak. His father makes it seem like he's always one failure away from being a disappointment to him, in ways that aren't fair.
On the other hand, we have Hiccup. Hiccup always goes after Snotlout even when he's disappointed, even when he has good reason to be angry at Snotlout. Hiccup is always there to help, always there to give counter-advice. It's Hiccup, more than any other rider, that acknowledges what it is that Snotlout has to deal with in his father, even when Snotlout doesn't fully understand what it is he's dealing with at all. It's Hiccup that let's Snotlout win when the competition doesn't matter. It's Hiccup that backs Snotlout's decisions when it should be Snotlout's decision to make. It's Hiccup that sticks around, that tells Snotlout through his actions that he's worth sticking around for. Hiccup didn't know that he was in a two-man war over the man Snotlout would become, but he was.
And then we get to Not Lout, where this has never been more obvious. Spitelout tells his son that his friends aren't really his friends, they're competition, all trying to get in good with Hiccup so they can be higher on Berk's ladder of power. And Snotlout essentially panics about this, spending the rest of the episode trying to prove that he's the better leader. He tries to prove that he ought to be higher on the ladder than he appears to be. He puts his friends in danger to prove this a few times in the episode and it all comes to a head in the emotional climax of the episode.
Like yes I know the scene I'm about to talk about takes place not even halfway through the episode but hear me out.
Snotlout barges into Hiccup's hut and tells him that he will not be left behind, he's "just as good, if not better, than the other guys" and he wants to lead the dragon riders when Hiccup becomes chief. This clearly lays out all of Snotlout's insecurities, and in response Hiccup says "Okay, but you can't force yourself into a leadership position. There are things you need to work on." And he proceeds to tell Snotlout that each dragon rider has their expertise. Astrid and battle strategy and Fishlegs being a dragon encyclopedia. Snotlout needs to either grow his capabilities in all the categories, or learn to look to his friends to help fill in his gaps so be can maybe make better decisions for the group.
Snotlout takes Hiccup's words the wrong way, but the seed's been planted. Hiccup literally just laid out for him that if he wants to climb this nonexistent power ladder, what he needs to do. If Snotlout wants to be the next Hiccup, this is the way to do it. And Snotlout repeats his father's philosophy, that Jorgenson's don't ask permission to be great, and leaves.
The episode proceeds with more of Snotlout being a bad leader and Hiccup gives Snotlout the opportunity to lead a training mission, which goes horribly. Snotlout gives up on himself, grounding himself from future missions. He can't gain his father's approval by climbing the ladder, and in his mind he can't gain Hiccup's approval either because he just failed massively.
The rest of the gang go on a mission to get rid of the Hunter's stash of dragon root, and they become in great danger. Snotlout catches onto a trap, shows up, and in the heat of the moment, successfully leads them all out safely. He deals out tasks to those who are best suited for them, he's determined in his position to protect his fellow riders, and he goes out of his way to protect Hiccup, the one guy who more so than any other in the group doesn't seem to need the protection and ends up saving his life. He lead and he did it well. Snotlout gains Hiccup's praise when Hiccup tells him that he saved his life and it's a good moment, but it's not the emotional resolution.
The following scene, the last in the episode, is so beautiful to me. The riders are finishing the job on the ground and Hiccup and Snotlout are in the air watching. Hiccup tells Snotlout that he's proud of him, that today he did good as the leader Snotlout said he wanted to become, but who knows what the future holds. Hiccup implies he can't promise him that when he becomes chief that he'll give Snotlout the leader of the dragon riders position. And Snotlout says, yeah I've been thinking about that. "Whatever greatness I end up doing, and trust me, it will be great..." and he laughs a bit, "it's gotta be what I want to do. Not what my dad wants me to do."
And the music in the background sounds like the lightbulb turned on. Snotlout realizes that his father doesn't really know what he should be doing with his time, or his life. His father has consistently given him bad advice and caused him to do things against people he cares about to fulfill these goals he never really set for himself. And all the while, Hiccup and dragon riders have been patient with him. They never abandoned him. Because they are his friends, and they love him and want what's best for him. And maybe he feels that now, he lets himself believe it. He will be great, not with Spitelout's permission, and not with Hiccup's, but he will be living in Hiccup's world. Hiccup will be chief and he's already changed the world they live in to create his own. A world of peace where they can ride on dragons. And Snotlout wants to be great inside this new world, standing next to these great people he gets to call friends, and be one of them, not under them or above them.
And Hiccup sees this in Snotlout, he smiles and says "You know, we may not be so different after all." And he doesn't need to explain what he means, he just flies away, and Snotlout knows.
Snotlout's face in those last frames are such a thing of beauty, at first there's confusion as he takes in the words. Then, a large smile, as he realizes what Hiccup meant. That Hiccup too dealt with his father wanting him to be something he wasn't and now he's made himself great, and it's in something he wanted to do. And finally, a quick look of determination as he too flies away to follow Hiccup into the sunset. Because Snotlout did it, he gained the only approval he needs. Approval as a friend, a comrade, as someone worth taking with you into whatever greatness you achieve.
And when they fly into that sunset together, with all the dragon riders into the great beyond, it's Snotlout at Hiccup's right side, a place he will consistently want to be until the end of the story. Because in this episode, Hiccup won. Snotlout no longer wants to be the man Spitelout appears to want him to be. He'll be his own man, and he knows Hiccup will defend that with him.