Aside from Stoick commissioning him to, why would Bucket display Hiccup as overly buff and manly? He could have symbolically depicted Hiccup as what he, his father, and a good deal of Berk envisioned him as in reflection to the events ofthe movieand handling the threats of the show the same way. It is a common thing for artists to have done this, and Bucket was really getting into perfecting the image he had in mind for the portrait.
In "Alvin and the Outcasts", it seems like a piece of bad luck that the Outcasts happen to show up exactly when Berk is at its weakest. Then Mildew turns out to be a defector in "We Are a Family", and suddenly that coincidence is anything but. If anything he could have destroyed the armory to both make it easier and blame the dragons.
Only thing that would disprove that theory is the fact that Alvin wasn't aware that the armory was destroyed till he got to Berk and saw the evidence himself. Otherwise he probably would have brought his fleet with him and went ahead and conquered Berk.
Astrid is really riled up about the Flightmare, to the point where she almost kills Snotlout twice in a fit of anger (one time by throwing her axe, another by hurling him to the ground and stomping his face with an axe in hand) as he makes remarks about the Hofferson family freezing in fear. Besides explaining even more so why she was so determined at dragon killing in the movie, its quite Viking-like for Astrid to be so serious about family honor because such was a bigfuckingdeal for Vikings to uphold. Snotlout is lucky it didn't turn into a duel over it because in the state she was in, pieces of him would be scattered across the islands.
This also would explain her hostility at Hiccup's badass level grinding in the movie. She felt he was going to be a threat to her plan to redeem the family name by being the first in class and get the chance to kill a Monstrous Nightmare. In a way, it's possible her massive effort in improving the Academy was another way to redeem honor.
A bit of historical subtext: It was extremely dishonorable for Vikings to let any harm come to a woman or children, to the point where they would not attack the house of a sworn enemy until any women or children had left. Lack of courage is humiliating for a seasoned fighter, but the nastier jokes would have been stopped by a simple order from Stoick to be polite to his grieving family. However, an accusation that Finn would fail to defend his niece would certainly hold up for ten years, particularly without evidence to disprove it. Luckily, he was proven innocent.
Dagur likes knives. Dagur sounds like dagger.
The reason why Berk knows a lot about the Skrill, yet not how to handle it, could interpreted as being due to their former peace with the Berserkers under Oswald the Agreeable (who withheld some information).
The reason we don't often see Thornado in the show is most likely due to the fact that despite his introduction episode showing him and his fellow Thunderdrum living in cave. Thunderdrums are predominantly an aquatic species of dragon. He probably spends most of his time not giving Stoic a ride swimming around the waters of Berk.
This may be backed up in "Tunnel Vision". Stoick goes to get Thornado when the Whispering Deaths are attacking Berk. He seems to take awhile longer than he probably would if Thornado was somewhere 'in' the village.
Rewatching the series, it's clear that from the start Toothless showed traits of leadership even amongst the dragons... alpha traits, from trying to stop Hookfang gone berserk and keeping him contained to recognizing that Torch was taken from its mother, to leading them in saving the riders in Animal House. He was already becoming an alpha dragon as Bewilderbeasts were supposed to be.
Valka made Hiccup a dragon doll when he was little. A small hint about her backstory way before the second movie was released.
How many other Vikings had their honor stained because of some fancy trick that a dragon has like the Hofferson's were dishonored by Fearless/Frozen Fin Hofferson rather than any personal failures?
The Screaming Death has destroyed at least four islands worth of dragons. It's still alive, still growing. Just how terrifying will it be once fully grown, and how many more islands will be destroyed? Just what will it do when it goes for Berk, or if it heads for any other settled island? How many dragons died when it brought those islands down? Not all of them would of been full adults able to fly as Gift of the Night Fury showed us...
Best case scenario is by the end of the second season the screaming death may move to the shoreline of a continent or island larger than Berk. If it does it will still cause a lot of damage but the surrounding landmass may survive.
Think "In Dragons We Trust" was a Tearjerker already? How about this; Toothless can't fly, and likely hunt for food without Hiccup. Exiling him is likely to be tantamount to a death sentence and Hiccup probably knew this. Although Toothless seems fine a day or so later when they reunite, be glad that it only for that short a time...
I highly doubt the other dragons would have left Toothless to starve.
What happened to the three Whispering Deaths that followed the Screaming Death? It's entirely possible that the Screaming Death ate them when they were unable to provide it with food (or the food they did bring was no longer sufficient). That would explain why the Screaming Death was alone in all it's future appearances...
Actually, the finale showed the Screaming Death really loved his family, and probably ate rocks and clay beside fish.