In "Valiant", after Arthur knocks off Valiant's helmet during their duel, he decides to take off his own helmet to even the odds. Everyone in the stands cheers, because they know THAT'S the kind of thing a noble knight would do.
In Episode 4, Merlin is poisoned. The guards, at Uther's command, all pull out weapons. Morgana? Morgana has a large, very sharp, chicken cutting knife!. Given what this woman can — and, in fact, will — do, it makes it both awesome and pant wetting at the same time. Screw the guards, it's Morgana I'm worried about!
Merlin gets one by drinking the poisoned cup.
One for Uther in "The Gates to Avalon," in which he spectacularly shoots down Arthur's proposal to allow him and Sophia to marry. Particularly notable in that most of the time, Uther is just a bitlackingin thesympatheticportrayaldepartment. If Sophia had been portrayed as even slightly sympathetic, this would have looked totally different — but because the audience is already aware that she's actually a Sidhe in human form planning to sacrifice Arthur for her own means, watching Uther tear into his son for being an idiot was extremely gratifying.
Merlin gets one when he defeats an entire group of raiders invading his home town with a miniature tornado.
Will: There's too many of them! Merlin: Not for me.
Will gets a CMOA for that episode. Despite having professed his dislike for Arthur he pushes Arthur out of the way of a bandit with a crossbow who wasn't quite dead yet. Then, while dying, he covers for Merlin and takes the blame for the mini whirlwind.
Also, Gwen saving Merlin's mother by hitting her attacker over the head with a shovel.
Merlin also kills Nimueh, one of the few villains in the series to be more powerful than him, with a lightning bolt, defeats an entire group of sorcerers trying to kill the king, and kills a sorcerer who has been training his whole life and just destroyed Gaius in less than 20 seconds.
Merlin killing Nimueh should get its own entry, because it really does require elaboration for you to get how awesome it was. To set things up, Nimueh has pushed three of Merlin's Berserk Button (his best friend, his mother, and his mentor), and he's finally had enough and fires a magic bolt at her. She absorbs it easily, mocks him about his "childish tricks" being useless against her, and throws a fireball at him. He dodges, and she sends the second straight into his chest, leaving him for dead on the ground with a smoking hole in his shirt. Then no less than three of these kick in in less than a minute. All are done without a single incantation, which gives us the impression that these are Merlin's instinctive abilities.
Merlin gets up, completely unscathed, from a fireball to his chest. And this was before he became a dragonlord.
After delivering a Pre-Mortem One-Liner, Merlin lifts his hand towards the sky, summoning a massive storm. Then he pulls lightning down from the clouds, striking Nimueh repeating with it until she explodes in a flash of light.
Rain falls down from the clouds, and somehow Merlin harnesses the power of the Old Religion to trade Nimueh's life for Gaius'. No artifacts, no incantations, just Merlin manipulating an age-old magic by sheer force of will.
Season 2
Gaius finally telling Uther off for the brutality of his anti-magic crusade in "The Witchfinder." Basically, any time Uther gets/almost gets what's coming to him.
Possibly defeated by Merlin's defeat of the Witchfinder. Through genuine cunning and a few well-placed spells, he manages to get him accused of being a sorceror himself, exposed as a fraud, and thrown out of a window. Oh, and he makes toads come out of his mouth.
Morgause's entrance into Camelot: Walking clad entirely in armour, killing a number of knights on the way in, challenging Arthur to a duel -Then removing her helmet.
Arthur attacking Uther in "Sins of the Father," blaming him for his mother's death and telling him that magic is not evil. Awesomeness is somewhat dulled by the fact that later, Arthur forgives his father and blames magic for deceiving him.
Episode 8 of Season 2. CMOA for both Merlin and Uther. Uther for not drawing his sword on his son who then attacks him, he then proceeds to keep Arthur at bay. Merlin then gets HIS CMOA for breaking in to the room and managing to calm a previously completely homicidal prince down even though the death of Uther would make things far easier for Merlin.
In episode 11, Mordred pulls off a feat that is both creepy and impressive for a child his age. Mordred is trying to escape from Camelot's guards when Merlin betrays him by magically tripping him up, forcing him to have to stop and fight. He magically levitates some nearby spears and runs the men through with them, killing them instantly. Before he leaves, he turns to glare at Merlin and gives him this warning that sends a shiver down Merlin's spine:
Mordred: I shall never forgive this, Emyrs, and I shall never forget.
The finale of Season 2. Even though he's devastated by the recent loss of his father, and previously his magic hasn't worked on the Great Dragon, Merlin faces and defeats a centuries old dragon. Then, instead of killing said dragon he sends it away, showing mercy even though the dragon has been killing innocent people.
Season 3
Merlin riding the dragon. The dragon is his bitch now.
The moment when Merlin wants to tell Arthur that Morgana is a traitor, only to find she has somehow spun it to make it seem like she saved the day. Morgana gives him a 'You can't beat me, Merlin' look from across the room, and he gives her an epic 'Oh yeah? Bring it' look right back. And not a word was spoken.
Gwen is out shopping with Morgana when she sees the disguised Morgause reflected in the mirror behind her, followed swiftly by Morgana clearly lying about what she was up to with "the old woman" of a few moments ago. Gwen keeps her cool, smoothly bluffs Morgana into thinking everything's fine, successfully conceals herself in Morgana's chambers and sees her practising dark magic, and then goes straight to a Reasonable Authority Figure to share what she knows. In a show that so often pushes the Reset Button and seems stuck on Status Quo Is God, it's immensely fitting that sensible Gwen is the one to finally refuse to ignore the obvious.
Topped only by her magnificent poker face in 3X13, when she assures Morgana that she's loyal to the new regime.
When Morgana and Morgause's army finally invades and takes over Camelot. Uther is forced to his knees and can do nothing but rant that Morgause has no right to do this, having apparently not heard of the right of conquest. Then Morgana simply enters the room, pointing out that she has a legal right to the throne. Suddenly it dawns on Uther that Morgana knows the truth of her birth, has been his enemy the entire time, is on Morgause's side and has achieved what no other villain or sorcerer could do, by finally overthrowing him. She takes her place on the throne, looking fantastic in her new crown with Morgause looking on proudly. Cut to Arthur and Merlin watching on and Merlin is eyeing Morgana the way a cat eyes a mouse it is about to devour.
Pretty much all of 3x13:
All the heroes get their very own Crowning Moment of Awesome in 3X13:
Arthur says "screw the rules" and knights Gwain, Elyan, Percival and Lancelot before leading them into battle.
Gwen breaks Leon out of prison with blacksmith skillznote Yes, we used the Z! and smuggles him out of Camelot in a dress.
Leon outright defies Morgana and Morgause to their faces, states his unwavering loyalty to Uther and Arthur and goes as far as to smirk at Morgana mockingly when he believed she was about to have him executed. He later, with the help of Gwen, escapes prison and joins Arthur in his rebellion against Morgana.
Lancelot covers Merlin's back on his mission to destroy the Cup of Life against immortal soldiers.
Percival turns up the hell out of nowhere and causes a rockslide that saves the loyalists from Morgause's soldiers.
Gaius gets the first blow against Morgause with his often-hinted at but still completely unexpected command of magic.
Elyan is the first injured in the battle in the cells, but the first to jump back into the fray despite the fact that he hasn't got any armour.
Gwaine just...exists.
Merlin retrieves Excalibur, kills at least twenty immortal soldiers with it, quite possibly kills Morgause, and destroys the Cup of Life.
In a little bit of Fridge Brilliance, now that Elyan is a knight, Gwen is sufficiently highly-ranked to be a perfectly legitimate partner to Arthur. Their first fully-public kiss is just another jewel on this Crowning Episode of Awesome.
Well done, everybody. You totally deserved that slow-motion Glory March into Camelot.
Season 4
Gotta give Morgana her due in the opening. She takes down four soldiers with magic, killing two of them.
Merlin is pretty awesome in the premiere, despite the issue that he's fighting an enemy he can't even use magic against. The fact that he went up against them at all is remarkable.
He doesn't just go up against them. He jumps in front of one so it will attack him instead of Arthur. And this is after Gaius has told him that no mortal has ever survived their touch. Bad. Ass.
In the same episode, Percival abandoning his torch—the only weapon against the Dorocha—to save three kids. And then Elyan shows up in the nick of time and saves him.
After Agravaine orders the city gates to be closed during a time of crisis, Gwen confronts the council and reasons that the refugees are bringing their own food to barter with the villagers, and that the city resources will only have to hold out for three more days before Arthur succeeds in his quest. Despite Agravaine, Gwen gets the entire council on her side, and wins the argument. That's the future queen right there!
The Wicked Day: Uther recovers from his Heroic BSoD long enough to take down the assassin threatening his son. And he has been bed/chair bound for a year at least.
Uther: It will take more than a coward like you to kill my son!
In Aithusa, when Merlin's trying to stop Borden from taking the dragon's egg. As awesome as it sounds.
Borden: What do you know? Your are but a serving boy!
Merlin: I am the last Dragonlord. And I am warning you: leave this egg alone.
Bonus points for saying it in his Dragonlord voice and then blasting the guy into the wall.
Queen Annis has one at the end of His Father's Son. She delivers a magnificent "Reason You Suck" Speech to Morgana telling her how bitter and twisted she has become and how she mistakenly allowed herself to be taken in by Morgana's lies. She then delivers the real pay-off line:
Annis: You came to me in the name of Gorlois. But I fear that you’re more like Uther than you realize.
In A Servant of Two Masters, Merlin (in his Dragoon disguise) dispatches the knights of Camelot. With haste. The best part: due to the effects of aging, he'd been having trouble climbing onto his horse. Three of the knights landed on top of each other, and he used them like stairs.
Gwen and Merlin in Lamia. Since the knights of Camelot were somewhatoccupied, it was their turn to shine.
Gwaine and Gaius staying behind in "The Sword in the Stone, Part I" so the others can get away with Arthur. The looks on their faces as Morgana's men approach are totally badass.
Although we sadly don't get to see it all, Gwaine's fights against Morgana's men. He's starving, beat up, and given insufficient weapons (like a wooden sword!), yet he keeps winning.
Arthur pulls Excalibur out of the stone in full view of all his people, thus proving himself a worthy leader and king.
Merlin's Dare to Be Badass speech beforehand. It's basically him saying. "Arthur, you're the Once and Future King of Albion, and you're destined to rule the greatest kingdom the world has ever known. Quit whining about how you aren't worthy. You ARE. Now go get your sword."
Merlin owning Agravaine and his men in the season finale. He decided that enough was enough and showed them exactly who they were dealing with.
Later he breaks into Camelot disguised as Dragoon, leaves a Voodoo Doll under Morgana's bed, and smiles quietly to himself during their confrontation scene when Morgana realizes that she can't call up her magical powers. And then when she's on the brink of slashing Gwen's throat, he sneaks up and sends her hurtling down a corridor backwards, once again proving that trying to harm Guinevere is the dumbest thing that any villain can ever do on this show.
Season 5
Opinions may vary big time on this, but Gwen sentencing her servant to death for treason was chillingly awesome. For one, the girl was actually guilty (which is impressive given Camelot's track record) and for another, sweet, mild mannered Gwen actually looked a little terrifying.
She also comes up with the plan to rescue Arthur's men from Morgana by going through Annis' kingdom. It probably would have worked if it wasn't for her servant.
Made better by the reveal that she never intended to execute Sefa in the first place. She was just trying to lure Ruadan there.
Merlin shows the spirit of Uther Pendragon that he has magic (and how he had always had it). gives the spirit a big "Reason You Suck" Speech about how Arthur is a much better king than he ever was, gloats a bit, and then throws him through a wall.
Merlin: Even while you were king, there was magic at the heart of Camelot.
Merlin's earthquake spell in Another's Sorrow. Especially notable since most of the time, Merlin's spells are small telekinetic moves (pushing/pulling things, bringing down a cave ceiling on Agravaine, etc), since that's what he can get away with. Seeing him unleash an earthquake with practically no effort reminds us that yes, this is the most powerful sorcerer of all time and Morgana has good reason to be afraid of him.
Merlin and Gwaine rescuing everyone in general. Merlin killing the guy right before he kills Arthur (and using a sword rather than magic) is particularly awesome.
And after that, Arthur vs. Odin. Truly a good end to their rivalry.
Elyan vs the magicked sword in The Dark Tower. And actually managing to win by tricking it into flying out the window.
Merlin using his mind's eye to find their way out of the forest. In addition to that, the Knights convincing a skeptical Arthur to follow him.
Arthur showing that no, he is not a total dollophead and actually deducing that Tyr was not acting alone, that someone in Camelot close to him is working with him, and that Merlin was not the one who poisoned him. Usually, he's his Genre Blind self, but in this case he shows that he's actually grown some brains.
Merlin and Daegal are trying to evade a group of bandits, when they get caught and surrounded. After it becomes clear that the bandits will not back down, awesomeness ensues.
Merlin: If you value your lives, you will not take another step.
Dragoon in the same episode. It is the first time he isn't remotely trying to ham it up, and you can tell Merlin means business. The subsequent scene with the Dochraid trying to threaten him, and failing, is also quite special.
The Dochraid tells Merlin that he will need all his strength to summon the White Goddess, and Merlin is wondering if he'll even be able to hold an aging spell for that long, much less summon a goddess. Not only does he pull it off, he's not even tired. As Gaius says, even years later Merlin underestimates himself.
Alator refuses to break under torture, and then tells Morgana it does not matter how powerful she is, or what she finds out: She will still meet her end at the hands of Emrys. Finna kills herself right in front of Morgana so that she will not learn who Emrys is.
Pretty much everything Merlin does after getting his magic back.
Wielding the crystals in order to see what Morgana's doing, and warning Arthur.
Going to the center of the caves to meet his destiny and enhancing his magic in the process.
Blasting his way past Morgana's barrier, revealing that he's aged up and looking ready to kick some ass.
Even before he got his magic back, Morgana wasn't willing to fight him, and he still managed to wound her.
Merlin showing up to the final battle and wrecking the army with lightning.
Sir Leon - who always seemed like the knight most likely to die in order to demonstrate how dangerous a situation was - survives the show. He's even given the very last line!
Guinevere outgambitting Eira by giving her false information, and then demonstrating that she's not as soft as she seems by executing her.
Gwen should get credit for being the only person in Camelot ever to figure out for herself that Merlin had magic rather than being told or catch him in the act.
Merlin is the most powerful warlock of all time, and despite being relatively untrained, he beats people in the league of Sigan, Nimueh, Morgana (while in his ancient form as well, making him much physically weaker than her, Morgause, Mordred, and the great dragon.
This also involves any scene in which Merlin fights without magic and still handles himself fairly well. The fighting leading up to the tornado in The Moment of Truth, and the Good Old Fisticuffs in the bar brawl in Gwaine were notable examples of Merlin subverting the Squishy Wizard trope.
in the sympathetic portrayal department. If Sophia had been portrayed as even slightly sympathetic, this would have looked totally different — but because the audience is already aware that she's actually a Sidhe in human form planning to sacrifice Arthur for her own means, watching Uther tear into his son for being an idiot was extremely gratifying.