The Hero gets one with at least every Chaos Lord fight. This includes:
Escherion: Using a mirror shield to deflect his inversion spell back onto him.
Vath: Throwing his sword at the Chaos Dragon Amulet and destroying both in the process — but really wanting to skewer him with it — and also riding on Stalagbite to destroy the Rock Roc
Kitsune: Fulfilling the Dragon Koi prophecy by jumping higher and higher up a waterfall of Yokai in order to close the rift with the Hanzamune Dragon Koi Blade, and then sending Kitsune back to the Yokai world by accidentally opening a rift with the sword while trying to hit his invisible form!
Wolfwing: If one chose the Good decision, the hero brings a speech to convince Wolfwing to be good. Plus they even point out that even if Wolfwing tried to unite the Werewolves and Vampires, he'd still have to worry about other invaders.
Kimberly: The epic fight against her Chaos Beast, then fighting off her band.
Ledgermayne: Pretty much standing up to him even when Ledgermayne pretty much destroyed the last item for the Arcane Staff.
Tibicenas: Using a genie's wish to depower him and then beating the ever-loving crap out of him.
Then there's all the times when players crash the systems or lots of players coming in. These include:
The first ever Friday the 13th event which caused the game to SHUT DOWN for 10 minutes cause there was at least 29,000 players trying to get on at once.
The Mythsong finale with 31,000 players also counts.
Or the time all the players helped lift Battleon off the ground...twice!
Artix in the Doomwood Saga. Normally a undead-slaying paladin, he's got Spirit Orbs channeling through him, can beat a dracolich without his Blinding Light of Destiny. That is because he is an Undead Slayer, whose job is to free the souls of those made into undead and help them find peace in the afterlife.
There's also his destruction of Vordred's armor of skulls through means of unleashing the power of all the Spirit Orbs held hostage by Vordred, since once Artix frees a Spirit Orb, it cannot be re-enslaved, no matter how powerful the would-be enslaver. This sets the stage for Vordred's ultimate defeat.
Drakath gets one too. Crashing Shadowfall into the ground, and saving the Hero twice in the Arcangrove saga.
Any cutscene with Drakath in it can qualify actually. This trope's favorite? Here.
A Real-Life example: Artix Entertainment is known for helping out charities and auctioned off a full Xan poster with autographs. It got sold for $15,000...but it was a scam and the person just wanted to do it for no other reason than to be a jerk about it. Then, a player came in and not only bought the poster for said price, but also gave an additional $2,000 for the whole thing. He was rewarded by meeting the group and a special customized avatar for his kindness.
The finale for Doomwood: AdventureQuest Worlds brought out their best with 5 multiple endings, back to back boss fights and a sign that we haven't seen the last of the Doomwood characters.
The end of the Shadowfall War has recently given a Moment Of Awesome to Chuckles, the only undead that Noxus' magic did not turn against Gravelyn because he was Gravelyn's own creation, who freed Gravelyn and knocked Noxus off the Shadowscythe throne while still a disembodied skull. And Gravelyn rewards him for this after you defeat Noxus by putting him in Noxus' body!
The Etherstorm War. A three-way war between good, evil, and Desoloth to decide the fate of Desoloth the Final. Evil won within 48 hours, with the other two factions stayed at least 20 percent behind evil throughout the entire war.
Doomworld Pt 2's finale. We have Gravelyn unlocking the power of the Champion of Light and actually purifying the Doomblade. Then we have her announcing that she is the Empress of Shadowscythe and how she is going to make Vordred a soldier to the Shadowscythe Empire.
It gets better. She goes head to head with Drakath himself over the skies of Battleon and actually hurts him in a fake universe he created himself and stated he was invincible in.
The entire Artix Entertainment fanbase has gotten one in the 10th Anniversary Event by stopping Operation Gameocide, taking down millions of EbilCorp drones released by Chairman Platinum into every one of Artix Entertainment's major games to prevent the complete shutdown of Artix's game network. This despite Platinum releasing 2,000,000 extra monsters as the war progressed.
In the Bloodtusk chapter, Khasaanda, believe it or not, gets her own Bad Ass moment after getting sick of all the times her fellow trolls laughed at her, using her power to steal Krellenos' Chaos powers and add them to her own and replace him as a Chaos Lord, and then proceeding to strike him down, even when The Hero tries to stop her, which she prevents by psychically holding them in place, all while telling them that it was a family matter, and that they weren't her family. Considering all the crap that Krellenos put all of Bloodtusk itself through, and his murder and Chaorruption of their own younger brother Antiphuus, this was a satisfying fate for a monster like him.
The Chaos Finale has awesomeness in spades:
It starts with the Hero, having just gotten curbstomped and killed by Drakath, battling through the Underworld and lending their power to raise the dracolich fortress of Shadowfall so that Gravelyn and the Alliance can do battle with Drakath and all his forces.
Then, in order to get the hell out of the Underworld and back to the land of the living to battle Drakath in person, the Hero tracks down and kills DEATH HIMSELF. The last time Death got deaded during the second Doomwood saga, it resulted in a Zombie Apocalypse upon Lore. But since the Hero and Death switched places for a while in an earlier storyline, the Hero has now become the new Death. Holy shit doesn't even begin to describe it.
The first clash with Drakath in the final showdown not only results in the Hero pulling Gravelyn's ass out of the fire in true Big Damn Heroes fashion, but in RIPPING OUT DRAKATH'S RIGHT WING!
Drakath gets some evil badass moments as well, namely one-shotting both the newly-returned Stalagbite and frigging VORDRED HIMSELF.
The Hero, having been awakened to their true power as both the Eternal Dragon of Time and Death, is not only able to fight Drakath, the Champion of Chaos himself, on equal footing, but take him down despite Drakath going One-Winged Angel in a final bid to destroy you. And since there is only one more release remaining for the saga, only one task remains — entering the Portal of Chaos and throwing down with the Mother of All Monsters herself!
Not yet... you gotta save the world from the awakening of ancient titans and formerly dead evil beings... on a whole new continent.