In Secret of the Omnitrix, Gwen gets dragged underground by a pack of Florauna (Wildvine's), and the male half of the Bratty Half-Pint duo proves that he'll risk the universe for people he cares about:
Ben: Going hero!
Myaxx: Ben, no! The self-destruct will accelerate!
Ben:I DON'T CARE!!
Ben's first transformation into Way Big and utterly obliterating Vilgax's entire army singlehandedly before hurling Vilgax into space. In canon with Alien Force, this was Vilgax's final defeat in the original series.
From the same episode, Air Upgrade (melding with the contents of a junkyard to create a functioning space rocket!)
More Cannonbolt awesome: At the end of "Grudge Match", Evil Counterpart Kevin has Ben cornered, smugly declaring he knows all of Ben's aliens and nothing he does can surprise him. Ben then turns into Cannonbolt, an alien Kevin hasn't seen before, and spends the next thirty seconds effortlessly smacking him around.
Connonbolt: "New game: it's called Dodge Ball!"
Earlier against Kevin in "Framed," Ben gets a more low-key Moment when, out of a mixture of pity and disgust at the boy, Ben simply refuses to fight him, a complete reversal of his usually violence-happy persona, and coldly remarks that Kevin isn't worth the effort.
It seems Kevin just provokes awesome in Ben, as he gets another Moment against him in the Twenty Years Into The Future episode "Ken 10". Kevin, in a brand new One-Winged Angel form, spends a good five minutes pulverising his old foe, and nothing Ben does works. Then Kevin hurts Ben's son. Big mistake. Ben promptly turns into the monstrously huge alien Waybig and pounds Kevin into the ground. Again. And again. And again. It's surprising he wasn't putty after that.
This troper seems to have it for Guitar Moments, but in the episode with the evil sentient weather machine, Ben goes up and uses a guitar as Four Arms, but then is turned back into a human, and STILL manages to defeat the weather machine with the power of rock! And after the weather machine is defeated, Ben SURFS DOWN THE WEATHER MACHINE ON A GUITAR!
In this troper's opinion, Ben's best Moments of Awesome are when he finishes the job just as his human self. Like against Ghostfreak or Kevin in Back With Vengeance. After seeing Ben's aliens do all the cool stuff it just becomes so much more awesome and surprising to see that regular Ben can be pretty capable on his own too.
Saving Kai is also pretty good. The Omnitrix refuses to work, so he just hops over buildings, jumps on a barrel, grabs Kai, and jumps for an awning. That goes into the hero book, no matter what ANYONE says.
Four Arms vs Retaliator in "Destroy All Aliens". Especially the part where Four Arms catches missiles, and, after a bit of experimentation, uses them to fly.
Ben gets serious in "Last Laugh" when he sees what happened to Gwen when Zombozo sucked her soul out. He transforms into Ghostfreak and freaks Zombozo out, especially with that scene where he reveals the tentacles.
Ghostfreak: "I've just figured it out; there's something I'm more afraid of than you. Losing my family to some goofball emotional vampire. In other words...you're going down, clown."
Impaling and murderingMonster of the Week Slix, preventing him from killing Ben... then proceeding to attempt to kill Ben himself.
His Evil Plan in "Framed." He usually just acts like a super-powered beast, so seeing him actually have a thinking plan that hits Ben where it hurts most (his pride) is quite impressive. His newfound scheming later resurfaces when he attempts to betray Vilgax at the opportunite moment in "Back with a Vengeance".
This development is taken to it's logical conclusion with Kevin 11,000 in "Ken 10". Gone is the angry, emotionally unstable kid from the past...as an adult, Kevin 11,000 is chillingly composed and calculating, and manages to be awesome despite how evil he is.
Turning on her Uncle Hex at the moment he's about to become all-powerful, so that she can have it all for herself. As she puts it to Hex, "I get the charms AND the power and YOU get SQUAT!" That's always the kind of thing a good Bastard Understudy should hope to achieve.
Charmcaster and Gwen have a magic battle in "Ben 10 vs. the Negative 10: Part 2". Rojo attempts to interfere and attack Gwen...prompting Charmcaster to join Gwen in blasting Rojo away. Charmcaster clearly takes The Only One Allowed to Defeat You trope seriously!
Defeating Ben just by touching the Omnitrix insignia.
Being able to break Diamondhead.
Destroying Mount freaking Rushmore. With Ben's FACE no less.
His first battle as Swampfire. Or the part of the battle right before that when the Omnitrix refused to work and he had to fight as a human. It's hard to decide which is more awesome.
Talking down two bullies in Tranquil Fury and getting applause from all his peers for doing so.
Ben over and over again in "Darkstar Rising." First, after a Plumber effortlessly whips around Kevin, Ben restrains him just as fast as Goop. Then he saves Kevin and Gwen Big Damn Heroes style, resists Darkstar's energy drain to the point where he says "I forgot how strong you were," and finally all but kills Darkstar by going from one alien morph to another despite the energy drain it leaves on him.
"Voided": Ben's skydiving moment that appears to be a Heroic Sacrifice and results in Big Chill freezing Devoid's furnace, turning into Humungosaur and literally squashing Animo with his fist like a bug, and his semi-Ninja fight with Pierce where he lets Pierce win.
"War of the Worlds". Winning the day, not with firepower, but with the peaceful method of helping the Higbreed with their problem. Actually, "strength tempered with mercy" is a recurring theme in the episode. Namely: Using the Omnitrix to cure DNAliens, Ben stopping Darkstar from harming a bunch of them, Cooper using his technokinesis to build "DNAlien cure guns," and use of Non-Lethal K.O. as a combat tactic. That shows a real maturity that you'd hope someone with their level of power would display...and stick to.
Ben gets a one in "Con of Rath". While in the titular form of Rath, a 7 foot tall, super-strong, tiger-like alien, he literally leaps down the throat of a newly introduced villain, who is about 3 times his current size, jumps back out by punching out the villain's teeth, then jumps back on his head and threatens to do it again and come out with a sweater made of his ORGANS if he is to declare war with another alien race, all to save the other aliens' larvae marshmallow-like prince.
Rath telling off the ambassador that tricked him into the whole thing. He's not eloquent, but he gets the point across.
Rath: (to the ambassador) NEVER. TALK TO ME. AGAIN.
Ben threatening to let the Omnitrix self-destruct if Vilgax doesn't return it in the finale, capping off the Xanatos Gambit by being perfectly willing to let the Omnitrix explode if it means Vilgax can't have it. Then doing the same thing to Albedo. Even if it wasn't going to blow up the whole universe, it was still pretty badass.
Humungosaur: Guess what time it is? IT'S HERO TIME!!!
"Coming to my senses" and defeating Morningstar the sparkly vampire. Some of us have been waiting a long time to see that, girl!
Similar to her defeat of Morningstar, Gwen's defeat of Charmcaster in In Charm's Way. Charmcaster has taken her powers, so Gwen challenges her to a fist-fight. Charmcaster doesn't roll that way, so she instead blasts Gwen with magic...which is exactly what Gwen was actually anticipating with the fist-fight challenge, and thus Gwen reverses the spell, takes her powers back, and opens up a dimensional vortex and chucks Charmcaster and her minions in it.
"Inside Man" when he single-handedly saves Gwen from being sucked up into the DNAlien ship by pulling her back down to earth.
The episode where Ben is trapped in Alien X: While he was in his coma, Kevin used his power to absorb rubber, and effortlessly pwned the alien army trying to capture him.
Kevin, after being cured of his mutation in a decidedly painful way, stopping a crushing punch from Vilgax cold with one just one hand in "The Final Battle."
"Guess who's got his old powers back?" *Sends Vilgax flying with a single punch*
His defeat of Ghostfreak. After the massivevillain and badass decay he went through, Vilgax finally gets to be cool again.
Even a decayed Vilgax managed to Curb Stomp the "Max Force" (including Max himself!) without really trying.
The first battle between him and Ben is really awesome. Even if Vilgax lost, he put up a good show. Vilgax on the warpath is always something to see. Especially when he spends most of a two-parter fully mauling the hell out of every other hero we know with his new powers.
Ben & Riney the Highbreed WORKING TOGETHER to survive. This good karma comes back to him in the finale.
Ben's dad in "Grounded" with the Space Bazooka. Don't forget Ben smacking a Highbreed commander with the bazooka afterwards in his Humongosaur form. Seriously, the Highbreed was sent flying into a tank.
Julie standing on top of Ship, flying into a laser barrage, not the least bit concerned for her own well-being, in "War of the Worlds."
Tech-blob-alien-pet Ship gets one in Vreedle, Vreedle (aka, Don't Fear The Repo), when the Vreedle brothers (a pair of bounty hunters known for their over-violent tactics and tendency to never bring back a living target) come to retrieve and return him to the Galvanic Mechomorph that originally spawned him. Julie gets in the line of fire, so Ship takes matters into his own hands: he becomes a suit of Powered Armor to protect Gwen and Julie, gives the latter a fighting chance against the Vreedles, and help hold them off until Ben and Kevin get back from space-court.
Gwen defeating Zombozo without even having to fight. It was just... seriously, it has to be seen to be believed how awesome it was.
Ben rushing to Julie's rescue when Captain Nemesis/"Overlord" captures her, transforming straight into Ultimate Humongousaur, and proceeding to lay into him with everything he's got, without speaking a word (And note that since Alien Force, Ben usually says his alien form's name, which proved that he was dead serious with Nemesis).
And after several solid moments of getting his ass kicked into next week, Aggregor reveals that he didn't even feel a thing, and pays Ben and company back tenfold.
You know Psyphon, Vilgax's toadying sidekick? He'd be the last character you'd expect to have CMOA material. After one of Vilgax's many "final" defeats, Psyphon comes to Earth to avenge his master. He's got killer robots, he's got all the weaponry Vilgax had acquired before his "death," and he's got a serious mad-on. He was in fact the first villain ever to actually beat an Ultimate form - something Vilgax himself had yet to do. You'll spend half the episode saying "No way, he did that?"
Which brings us to Cash and JT using a giant alien energy-draining raygun to depower him and save Ben's hide. And nobody will ever know.
Admit it. Spreading himself as Goop throughout an entire water planet when Aggregor has stolen the very core that keeps the planet together and SUCEEDING at pulling it back through sheer force of will is probably the biggest feat Ben has accomplished so far.
Gwen and Charmcaster are just awesome all throughout the action scenes of "Where the Magic Happens". In the non-action variety, Charmcaster's speech of defiance to her father's killer toward the end stands out.
How is Ultimate Kevin pimp-slapping Aggregor and draining all his awesome powers not on here?
In "Forge of Creation" a ten year old Ben manages to guilt trip an insane, monstrous Ultimate Kevin into not taking the powers of a baby Alien X, even though he knows that Ultimate Kevin could squash him like a grape.
"Ultimate Power" is a bastion of awesome. To wit:
We finally get Gwen vs. Ben - and by golly, is it epic, with plenty of awesome exuded by both sides.
Later, Gwen vs. Kevin. She uses one of Charmcaster's summons on him. Gentlemen, the Les Yay from a few episodes ago has come full circle.
When they're putting the final touches on their plan, who should help but Cooper, who hit a major growth spurt.Took a Level in Badass indeed.
When Kevin shows up at Gwen's place, Max is there to greet him. He doesn't put up much of a fight, but man, does he kick some ass when needed.
A few seconds later, Kevin's stepdad shows up to try to talk him down. Kevin is about to raise his fist to his stepdad - a mere mortal with no magic powers or alien tech backing him up - and the guy doesn't flinch at all. Guess badass runs in the family.
The Sonic Doom attack that Ultimate!Echo Echo uses undoubtedly qualifies.
Finally, after all is said and done, Darkstar reveals that he just wanted to steal all of Kevin's powers for his own. It would seem that the series is about to invoke Here We Go Again...then Ben reveals the last-minute failsafe in his plan, which strips Darkstar of his newfound powers.
Added awesomeness coming from Ben actually saying 'Like we didn't see that coming', showing Darkstar's Chronic Backstabbing Disorder has come back to bite him.
Future Ben 10,000. To elaborate, Future Ben (BTW, the Ben 10,000 we saw in the original series was confirmed to have been an alternate version,) has only one form shown...Ultimate Ben. Basically, without actually BECOMING an alien, he can still use his Ultimatrix's alien's powers. He still has to switch between them, but man, is he awesome!
"The Purge" the Forever Knight, being turned back into a real treath by the return of Sir George start hunting aliens and attempting to kill them if they can't or don't want to leave Earth. Ben fight Driscoll in a duel, asking that if he wins, they will have to let the aliens go. Though he wins, Driscoll goes back on his word. Ben answers by stabbing the wall just next to his head as Ultimate Spider-Monkey, turning back to human, and delivering the following speech:
"Maybe you forgotten something: I'm Ben Tennyson, wielder of the most powerful weapon in the universe. I stopped the Highbreedinvasion, I defeated Vilgax in hand-to-hand combat and I've beaten the Forever Knights more times that I can count. Here's what's going to happen: you're going to release these prisoners, you're going to crawl back to whatever hole you came from and you're going to stop hunting down aliens because if you don't, I promise, you'll regret it for the rest of your very short lives."
Cue to Driscoll and his knight leaving without any more argument.
"Ultimate Sacrifice". Ben is willing, when faced with annihilation in order to let the now sentient Ultimates live, or planning an escape, he accepts dying for them, even telling Gwen he has no plan, he really is going to die. If it weren't for the fact that his willingness to sacrifice himself let the Ultimates out and stopped him anyway, as well as Azmuth coming to help, Ben would be dead.
In "The Widening Gyre", Way Big vs. the Garbage Monster.
"The Ultimate Enemy Part 1", George and Ben vs the Diagon powered Vilgax. Also, Kevin freeing Gwen from Diagon's mind control.
"The Ultimate Enemy Part 2": Ultimate Way Big. That is all.
After that, we have Ben stabbing Vilgax with Ascalon, sealing the Diagon in said sword.
Vilgax, even though Ben has beaten him, nearly gets moral victory when almost manipulates Ben into using Diagon's power to remake the universe to his own liking, only to be stopped by Julie.
Using Ascalon to turn the Esoterica back to humans.
Vilgax telling Diagon the universe is his to conquer was pretty awesome. Vilgax baiting Diagon into killing himself was also pretty awesome.
And last but not least, Ben doing the right thing restores Azmuth's trust about him being The Chosen One and he gives Ben a new Omnitrix.