Hiccup capping a demonstration of dragonriding acrobatics by gliding straight at a ledge, jumping off Toothless, running across the ledge, then jumping back on.
A meta example: Dragons are the strongest, most fearsome creatures known to Vikings. This tribe trains its children to ride them, and we have no reason to believethat this will change in the future. So in the future, this one tiny tribe will have warriors trained to ride winged, death-spitting harbingers of war from early adolescence.
Alvin and the Outcasts
Gobber splits a tree with a thrown kitchen knife, demonstrating that the vikings that they aren't entirely helpless against the invading forces.
Astrid gets a few:
Stoick trusted her with one of the few surviving axes in the village.
She knocks out Mildew, who was about to give up Hiccup to the Outcasts.
Then flinging aforementioned axe at Alvin's head when he wasn't looking. Yeah, he caught it, but she demonstrated that she was willing to take on Alvin without hesitation. Later, she also managed to take advantage of the steam the dragons create to knock Alvin about and effect an escape.
The fact that Alvin was able to catch said axe without even looking was a pretty sweet scene.
The Big Damn Heroes moment when she and Stormfly torched the arrows that had Hiccup's name on them.
Hiccup tricks Alvin into taking him to Dragon Island, where he then saddles Toothless and demonstrates that he's not to be taken lightly.
Stoick's fight with Alvin. The big guy finally has a physical match, but Alvin has the disadvantage of having tried to take Stoick's son, and gets himself anchored by the ship's mast for the trouble.
The dragons burning Alvin's ship. Notably, the one area this show tends to fail animation-wise is when the dragons breathe fire, but this was very well done.
Stoick letting Mildew know that he intends to let the dragons stay after all, seeing as how they saved their lives.
Hiccup gets another for calling out Mildew.
Hiccup: And I may not be able to prove what you did, but I will never forget it.
A rather subtle awesome moment is that Hiccup is recognized outside of Berk for his achievements of ending the feud between Dragons and Vikings, his ability to tame them, and The battle with the Green/Red Death. "Dragon Conqueror" sounds like the most fitting Red Baron title for him. He is just too modest and prefers "Dragon Trainer" instead.
In addition to Red Baron, he's a full on Memetic Badass. One of Alvin's lackeys thought he was "ten feet tall and had the strength of a dozen men."
As well as being hilarious, Hiccup dishing out snark to Alvin and his crew. These guys could kill him at any moment, and yet he's talking to them as if they were more like an annoyance. If there was any doubt that Hiccup was Badass.....
A villainous one is Alvin's introduction. His men are struggling against an army of dragons. His response is to throw them away, flip a catapult over single-handedly, and use it to shoot down a Nightmare. He then does an Unflinching Walk back to his base as two dragons' fire-breath hits the ground behind him.
How to Pick a Dragon
No one can deny that Stoick and the Thunderdrum fighting off red-eyed wild boars was pure awesome. Up to Eleven when they team up and wipe the rest out as dragon and rider. To seal the deal, Stoik chooses it as his dragon.
Another one is that the same Thunderdrum had little trouble dodging Toothless's plasma attacks, which hasn't been seen before.
And because Stoick has a dragon of his own now, it's a subtle moment of awesome in that the chieftain himself approves 100% of dragons and a way of life with them, he is essentially sponsoring bonding with them, meaning more Vikings are likely to try learning about working with them. This also renders Mildew's viewpoints entirely moot and even outdated.
The episode also contains a minor one about Gobbers work as dragon dentist. After he removed a Gronkel's bad tooth he uses it to cut the strong rope which held the dragon's mouth open, showing just how sharp these things are.
Portrait of Hiccup as a Buff Young Man
Hiccup takes on the challenge of solving an old puzzle that nearly ruined Stoick and Gobber's friendship out of frustration. Those two took a month before being stuck at the Beach stage. Hiccup? With some help of his friends (mostly physical) he solved it in a day, highlighting his talent as a Guile Hero coordinating his friends and their dragons. It also helps the puzzle was later discovered to have been created by a "Hiccup" himself. The teamwork makes it equal parts awesome and heartwarming.
A mild one for Thornado: Toothless was exhausted after carrying Stoick around for an entire day one episode earlier. Thornado has been carrying Stoick and Gobber for the better part of a day looking for the kids and is just fine.
Hiccup calmly declaring he was going to go on a hunt to find a Scauldron with Stoick and Gobber, knowing the creature could kill him easily. While this shows how much of a Badass he has grown to, the fact he is competent on the trip and showing himself as a capable Viking subduing the dragon without Toothless helping was just amazing to watch. It's as if he is a whole different person compared to the movies.
His casual reply to Stoick warning him not to get bitten: "I know, I know, I'll die within twenty-four hours, got it dad." This kid will do anything for his dragon.
There is also the fact that Stoick directly agrees with Hiccup's assumption of Mildew with the dragons getting ill (right after finding Thornado in the same situation). If you looked at his face during the visit and on the boat ride, it looks like he is waiting for an excuse to kick Mildew's ass or banish him.
And when Mildew tries to refuse to help, Stoick orders him to help "or I'll throw you overboard myself!"
The Scauldron is pretty badass too. Even with a proper, logical-sounding plan they couldn't milk it for venom. Thankfully, it bit Mildew.
Stoick also gets an Offscreen Moment of Awesome. He's gone for half the episode because he was meeting chiefs from other islands. These meetings are so dangerous he buys himself a new sword for the occasion (admittedly, as an offering to the host chief who gets mad if he's not brought a gift). Then he flies off and the merchant looks in awe and saying how amazing dragon riding is. It may have become normal for Berk but for other islands it is a breath taking feat. Now imagine the look on the face of the other chiefs when he arrives riding a Thunderdrum.
Doubles as an Offscreen Moment Of Funny given the chiefs of the other islands would likely have an Oh Crap expression seeing Stoick on a dragon. Given Stoick's good mood upon returning, he likely had few issues while there.
Heather Report, Part 1
Astrid gets several in in episode 10. Most notably jumping from Toothless onto Stormfly and wrestling with Heather in midflight and winning!
Heather Report, Part 2
Astrid continues leading the awesome parade, infiltrating the Outcasts and goes all Guile Hero on us. Hiccup must have been giving her private lessons on the style.
More impressive given it shows her development from trying to solve every problem with violence in the movie to employing social tricks and small gambits.
Going toe-to-toe with a Monstrous Nightmare, and beating it, thanks in part to remembering the trick she'd just learned from Snotlout. She also later manages to weaponize the dragon against Alvin by punching it in the face. Though she does apologize to it, first.
She's also become the first cast member to bond with more than one dragon. That in itself is badass.
Even happens in-universe. Alvin practically gushes at how cool it was that Astrid's Monstrous Nightmare saved her life of its own volition.
Heather gets one. She saves Hiccup and co from the Outcasts.
The battle between the Outcasts and the Dragon Riders of Berk was a great one to witness.
Especially notable since the kids didn't bring Stoick or Gobber in on the fight, and handled it on their own.
Hiccup handling the obstacle part of the final race pretty well despite Snotlout's physical advantage. He dodges the rolling logs as easily as Snout and is only slightly behind the bigger boy; his prosthetic leg not only doesn't slow him down, he actually uses it to brake when he slides down the rock wall! Snotlout even gets one for taking a small boulder to the face and shaking it off. But the crowner is the end of the race when Hiccup intentionally loses so Snotlout can save face with his father. Sure, he came in second, but he got a full-on kiss from Astrid for it. That is a heck of a consolation prize!
When Lightning Strikes
To prove a point he will do anything for Toothless, Hiccup decides to provide a demonstration himself that the metal is a lightning rod more than Thor being angry: By getting on top of a sail mast and holding a metal rod up. He promptly gets zapped directly on the head and falls in the ocean, but he survives and has no ill side effects despite a direct blow. Talk about determination!
Stoick, Gobber, Bucket and Mulch willing to take on an entire mob to keep them from Toothless. Especially impressive is Mulch and Bucket, who, despite considering joining the angry mob, declare, "We stand by the chief!"
When Hiccup falls into the water, Toothless instantly breaks out of the same kind of apparatus that held him in the film, and goes after his rider.
What Flies Beneath
Hiccup & Toothless VS the Whispering Death.
Even more impressive was that Toothless was mostly holding its own before he allowed Hiccup to ride on and help him fly. Combined, the Whispering Death did not stand a chance.
The Vikings tricking Dagur the Deranged with a fake dragon attack.
With nothing but HAND SIGNALS no less.
Don't forget Hiccup's performance, "saving" Dagar from the "vicious Night Fury". And Toothless letting Stoick pull on his tail to add to the charade.
One for the animators—they made sure in all shots of Toothless during the "attack" didn't have his artificial tail fin on, because of course Hiccup would have taken it off to preserve The Masquerade.
And Meatlug's "hug" command has battle applications, as Hiccup has assumed.
Hookfang starting the attack from outside the arena by climbing down on the chain-dome was pretty cool too.
Hiccup and Snotlout, on their own and with a flightless toothless, outwit the Outcasts on their home turf after falling on it on accident. It so bad that Alvin himself is aware of how embarrassing it is that two children arrived onto their island and kicked their asses. The two acknowledging the awesome on the way back. A few moments include:
Snotlout going toe-to-toe with the Outcasts, who are trained adults. One of the bouts was two on one! Turns out Snotlout can be just as Bad Ass as any other Viking if he really tries.
Hiccup still dropping snark while surrounded by Outcasts again.
Snoutlout arranging an ambush, on the fly, worthy of any strategist.
Snoutlout defeats the remains of Hiccup's escort with a rod meant to fix Toothless's tail.
Said rod was made by Hiccup and was so well made it worked despite whacking Outcasts senseless.
Hiccup jumping off Toothless onto the ship and landing in a ninja-stance. Incredibly cool when you remember how physically clumsy he usually is/used to be!
And remember, he has a prosthetic leg. It doesn't slow him down at all.
Gem Of A Different Color
Fishlegs finally getting fed up with Snotlout's crap, and scaring him into giving up the last Changewing egg. Fishlegs! Even gets lampshaded by Bucket.
Fishlegs also races a trio of utterly pissed off dragons, in order to save a baby careening down a hill - with some help from the others attempting to shoot the dragons out of the way, which means there's explosions in the background as well. He even gets a slow motion shot as he reaches out and catches it - it's one of the most badass scenes in the series.
A small one, but when Hiccup and Astrid are fighting, Hiccup actually manages to flip Astrid over him. It's not much, but that's some improvement from the village's weakest viking.
Stoick and Gobber grabbing Logs to beat Changewings with.
We Are a Family
Toothless escaping from the Outcasts by refusing to eat, then casually tail-whipping the guards stupid enough to remove his muzzle.
The Berk's crew taking Alvin's soldiers by surprise with the help of Johann and his ship was AWESOME!
On the villainous side of things, Alvin achieves Magnificent Bastard status in the second half of the two-parter. He has Mildew act like he is another disposable pawn so he will work with Hiccup and learn the dragon bonding and taming process. All while the main cast is unaware of what just happened.
We can add Mildew to this one, too. Not only did he have a hand in The Plan itself, but he also played his role to perfectio. He fooled absolutely everyone and now he trains dragons for Alvin.
All the dragons minus Toothless get one at the end when they work together to free Toothless and Hiccup. Meatlug, Barf and Belch keep the Outcasts at bay with their fire while Hookfang and Stormfly dive in to grab Toothless and his rider and carry them to safety. Even Hiccup is amazed and Astrid can only say that they took their training to a whole new level!
Live and Let Fly (Flight Club)
Hiccup continues his ascent up the ladder of badassery levels by not only defying his dad's ban on flight, but also being the one preparing for a potential war with the Outcasts. Bonus points for having the balls to call him out on exempting him and Thornado from the ban.
Fishlegs riding Toothlesss and keeping up with a Meatlug with Hiccup stuck to her.
Sinking the Outcast ship by essentially doing a flyby, attracting all the Outcast's weapons and knocking it off course, then demagnetizing Meatlug and dropping all the metal right on top of the ship. Even considered such in-universe by Gobber as one for Fishlegs.
The Night and The Fury
Hiccup facing down Dagur the Deranged in single combat, with almost no help from Toothless, and winning. Effortlessly, at that.
Heck, all the tricks in Hiccup's shield. It has a grappling hook and can turn into a crossbow.
Astrid dodging a full volley of spine shots from a wild Deadly Nadder. The Nadder was so embarrassed or annoyed that it just walked away.
A villainous one for Dagur, being smart enough to bring the armada with him.
The Screaming Death just screams badass. Like the Red Death, it plows through everything, shrugs off every single attack, and not even falling debris injuring its wings slowed it down.
Also, at one point it shoots fireballs like a machine gun.
Hiccup taking out the Screaming Death with a tactic similar to how he took out the Red Death... taking advantage of its natural traits to cause it to crash into a rock formation. Except instead of igniting its gas, he just lets it cause a landslide to cripple it.
Stoick grabs another log to beat the Whispering Deaths with, then having a Big Damn Hero moment with Thornado saving Hiccup. Gobber also gets right up to the faces of the Whispering Deaths, smashing them with a warhammer and blocking flames with his shield.
Fright of Passage
Hiccup and Toothless saving a paralyzed Astrid and later Fishlegs from the Flightmare.
The plan to divert the Flightmare? Repeated airstrikes by Toothless to blow a new channel for the water to flow while Meatlug sealed the old one.
Astrid showing off her Badass Normal credentials by facing off with the Flightmare on foot to distract it several times, keeping pace and doing some insane acrobatics.
Hiccup and Fishlegs trained Terrible Terrors to act as messenger hawks back to Berk.
The various dragons turned into refugees as their islands are destroyed get their revenge on the Screaming Death when Fishlegs and Astrid get them together and bring them to the Screaming Death, who proceed to Zerg Rush the thing until it leaves.
Special shoutout to Fishlegs for figuring it out via Fridge Brilliance in regards to territoriality.
Tuffnut, of all people, trains a massive typhoonmerang that's later revealed to be Torch all grown up. The tricks Tuffnut teaches him become very useful when they have to stop a forest fire. Heck even Hiccup is genuinely impressed by this.
View to a Skrill
Hiccup faces off with Dagur, who is using the Skrill as a weapon, in two-on-two combat (Hiccup/Toothless vs Dagur/The Skrill). Yet again, Hiccup wins with logic, causing Dagur to get electrocuted with the same cables he controlled the Skrill with, then Hiccup tricks it into knocking itself out by ramming head first into an icy reflection. The twins proceed to cause an ice-in to seal it in ice yet again with a large explosion in the glacial ravine it was trapped in.
Tuffnut bluffs his way around Outcast Island pretending to be 'Buffnut the Berserker'. As in, he fools the actual berserkers into thinking he's one of them.
The poem he composed on the fly was pretty good considering he had to make it up under pressure.
Alvin's death. He takes on Dagur and actually wins pretty well, then Dagur takes command of the Skrill and uses it to send Alvin overboard. As Alvin dives for cover, he proceeds to overcharge the water, leaving only bits of metal armor and blown up rocks behind to float back up, and the Outcasts are now under the command of the Berserkers.
Astrid, Fishlegs, and Snotlout take on three Outcast ships and essentially remove them from the fight for the duration, leaving Hiccup and the twins to fight the Skrill in the air.
Bucket and Mulch of all Vikings having a badass fight with the Berserkers trying to free the Skrill. Of particular note is Bucket. Who No Sells a club to the bucket, and sends a Berserker running with just a look after that.