The triangle button might as well be renamed the "Awesome Button", since pressing it causes you to do some pretty awesome things (like deflecting 10+ of Sephiroth's lightning quick swings in 1 second or cutting skyscrapers in half).
Perhaps one of the best is in Beast's Castle. Wherein you hop onto the chandelier, bring it down, smack it into the Dark Thorn, then swing it around and knock it on every single pillar in the process.
Pretty much any boss against one of the Disney villains. There's just something cathartic about beating up villains you remember from childhood, all while awesome music plays.
The final Roxas vs Axel fight. Throughout the entire prologue, Roxas has been having enough trouble using the Keyblade as it is, and is using the same three-hit combos Sora did in the first game. Doesn't help we have no idea who the guy is at this point. Then he duels Axel, who gives the famous "I'm SO FLATTERED" quote. Roxas responds by pulling out two Keyblades, becoming the first person in the series to use two at once, and becomes a spinning maelstrom of destruction with long, powerful multi-hit combos that can drain a third of a health bar.
The moment when Mickey Mouse unleashes a can of literal and proverbial shit onto Heartless and makes even Yoda look tame.
When Goofy "dies" and Mickey says "They'll pay for this,"; the way he throws off his cloak and gets his Keyblade is so epically awesome it's hard to describe. One thing you do know however, is that the Heartless are, most definitely, completely and utterly screwed by one incredibly pissed off and furious mouse who has a reason to viciously and violently murder them. He does
Maleficent letting the Nobodies attack her (and, to her credit, surviving their attack) to give Sora, Donald, and Goofy some time to run away. And promising that We Will Meet Again. She'd been going against them the whole time, and then that. Makes up for hanging around with Pete quite nicely.
Hey now, Pete himself gets to be Badass along with her when they pull a "Bad Guys Do the Dirty Work" moment in the final world. A huge swarm of Heartless is headed their way, and Pete yells "Bring 'em on!" before he and Maleficent rush into battle.
Shang knocking Shan-Yu over and then taking the Emperor in to safety.
The Storm Rider boss fight in The Land of Dragons, where you can hitch a ride on the boss's back.
Doubly awesome if you finish him off with the reaction command under his stomach, which causes Sora to deliver some quick strikes to his belly, send him flying into the air, and lands with a pose as the Storm Rider slams into the ground behind him and dies.
It might take him a little while to shake off his Heroic BSOD this time around, but once he does, The Beast is just as awesome as he was in the first game. A common complaint of this game is that the Disney worlds are mostly Filler, but Beast continues his streak of being relevant by personally helping Sora rip Xaldin apart, (with a little help from Belle's elbow).
For that matter, Belle's actions in general - rather than play the role of Distressed Damsel and force Beast to make a Sadistic Choice, she just has none of it and elbows him in the stomach, grabbing the rose and running to safety.
Auron's role in Olympus Coliseum is somehow even more awesome than anything he did in Final Fantasy X. He gets brought back from the dead by Hades to murder Sora, practically spits in his face in return, and goes off to team up with Sora and kick all kinds of ass.
Not to mention some of the lines he says to Hades.
And even after he's teamed up with Sora, it doesn't end there. When Hades makes Auron his slave by brainwashing him and forces him to battle against Hercules, he doesn't only keep his stance. He is winning, only minutes away from wiping the floor with Hercules when Sora and the party storm in and free him from Hades' control. Auron not only survives a battle against a super strong demigod, but he's kicking his ass without breaking a sweat.
Demyx's status as That One Boss can distract people from one major feat he pulled off: He managed to sneak into Mt. Olympus to steal the Olympus Stone. This bears repeating: Demyx broke into a place were gods live and stole one of their relics with impunity from the gods.
Though most of what she did in the first game was behind the scenes, Queen Minnie gets several crowning moment in this game:
She shows some extreme guts to threatenMaleficent of all people.
Minnie: You better stop right now if you know what's good for you!
Also not being a helpless escort during the Disney Castle mission and using her awesome but useful light attack, Faith, on Heartless in the Castle.
Well, there had to be a reason - other than the castle belonging to her anyway - that Mickey left her in charge.
Timeless River, sort of celebrating the past of Mickey Mouse before Epic Mickey did.
Being able to combo Past!Pete into Present!Pete to, in effect make him hit himself with a shockwave.
Just having Past!Pete fight alongside you against Present!Pete is awesome by itself.
No matter what the player thinks of Atlantica, the scene of Donald and Goofy rescuing Sora after he gets captured by Flotsam and Jetsam during "Ursula's Revenge" shows how far they will go to protect him, no matter the danger.
Port Royal, as a whole, is an extremely wholesome experience. You fight the Undead pirates, blast other pirates ships, essentially get a retelling of the movie and a sort of continuation on the second visit, fight Barbossa and an Aztec Grim Reaper Heartless as bosses, and actually see blood- even if its just a cut on the hand. Jack Sparrow is as cool as he was in the movie, even being able to wield a Keyblade for a short time; and it is interesting to see the stylised, anime-ish, and realistic characters clash (particularly Pete conversing with Barbossa).
The cutscene before the boss battle with Barbossa, where the heroes pull a Big Damn Heroes, there's a swordfight, and The Illuminator is introduced, letting Barbossa get a cool pose with it's Glowing Eyes of Doom.
Any time you summon Genie, it usually ends up being very spectacular. Especially since he mimic's Sora's drive forms.
Actually if you're proficient enough at Guard/Reflect (not that the game ever gives a proper tutorial on them) Prison Keeper is very manageable even at level 1. Which makes the fight more awesome in that you'll be deflecting his attacks back at him!
The boss of the second visit to Halloween Town, The Experiment, which shows how much research was put in as the creature is a mish-mash of background props from The Nightmare Before Christmas (for example, its right arm is part of the scenery in Dr. Finkelstein's lab).
Taking down the Groundshaker, one of the largest Heartless ever fought (only beaten by the World of Chaos) in the Pride Lands. What's more pure awesome is that Sora happens to be a lioncub here!
Pumbaa gets a quick one. On the second visit to Pride Lands, the ghost of Scar is haunting the land. While Timon is off getting Simba, Sora, and the others, Pumbaa is seen standing defiantly in front of Nala and staring down Scar's ghost alone in an attempt to protect her. Granted, he's shaking like a leaf and likely wouldn't have been able to do much, but it's still a pretty awesome moment.
The Hostile Program, which is one of the few bosses that isn't a Disney or Square Enix character, isn't in the main cast, nor is it a Heartless, Nobody, Unversed or Dream Eater, is fought as the boss in the firstnote or second, depending on whether or not the brief return to Hollow Bastion counts as part of the SP visit visit to Space Paranoids, and after which is where the game starts to heat up a little (YMMV on opinion though).
Tron smashing Sark in the face with his disk in Space Paranoids.
During the boss battle after this, once the MCP takes enough damage, Sark will sometimes put up a wall to stop the party from fleeing... which will allow Sora to perform a reaction command that will allow him to stab Sark in the head and instantly kill him! BIGMISTAKE, SARK!
Tifa willingly taking on Sephiroth. One woman. Bare-handed. Against a guy who habitually carries a ten-foot-long katana. And she holds her own. It's not out of the realm of possibility to believe that, had Cloud not fought Sephiroth, Tifa would have been able to beat him herself.
Sephiroth deserves one too. Even if you put all your effort into defeating him he simply brushes his shoulder and says, "Yeah you're pretty good." A far cry from when he was so simply defeated in the first game.
The Gummi Ship course "Assault of the Dreadnought", which pits your ship against a massive fleet of Nobody warships, including their flagship, the titular Dreadnought.
The mission itself revolves around you fighting your way through the Nobody fleet so that you can enter the Dreadnought and destroy the reactor core for its Wave Motion Gun. Not only will destroying the core get you some rare Gummi Blocks, you are also treated to a gorgeous view of the Dreadnought blowing up.
Sora and Roxas' Battle in the Center of the Mind. Everything about the fight conveys a powerful emotion of two souls meeting in battle to gauge each other and find answers.
The finishing move if you pull off the final Reaction Command in Luxord's battle: Sora pulls all the cards into his hand and sends them flying at Luxord For Massive Damage.
DiZ: Xehanort, Foolish apprentice of a foolish man. You have surpassed nothing- only proved how little we both know. We may profess to know the heart, but its essence is beyond our reach. We're both ignorant- as oblivious as when we began. I'm afraid any world you try to create, any world of yours, would be an empire of ignorance. That is why you and your creations are destined to fall!
Sora and Riku cutting buildings in half and throwing them at Xemnas. Really, the whole multi-fight sequence was just one Crowning Moment after another.
Also Sora and Riku reflecting the seven zillion lasers that Xemnas threw at them.
One for Riku when Xemnas captures Sora in a HP draining energy attack and the player swaps to Riku, who ends up negating Xemnas' attack, then beating him up and throwing him away from Sora, saving Sora's life in the process and then saying "Is that all you got?". Xemnas is even stunned after this happens.
Sora taking out a Magnum Loader after Donald accidentally grabs onto it while playing with a Light Cycle. Sure, everyone else enters a Heroic BSOD due to the required piece of data needed for the trio to escape is destroyed, but seeing Sora taking action before that is pure badass. Not to mention that he uses his Keyblade to repair the broken data.
It helps that Sora was wearing armor at the time, had a pretty angry face, and a Pre Ass Kicking One Liner that doubles as a pun. This scene is clearly showing how angry Sora would get if his friends got hurt in a non-humorous way.
In The Land of Dragons, Shan-Yu attacks the Emperor's palace riding Storm Rider, stopping Sora from reaching to Riku. As Shan-Yu is about to finish off the Emperor, Sora stops him. The Storm Rider? Down in one hit.
The clash between Past Pete and Present Pete would have to be even better than the game version, especially when Past Pete, furious at his present self for littering his river (by throwing the Cornerstone of Light in), delivers a finishing punch in retaliation! Present Pete was wise enough to flee Timeless River before Sora and the gang, who were waiting right behind him, would beat the snot out of him!
Kairi is facing Saix; who plans on using her as The Bait to attract Sora. He tells her that all she needs to do is scream; and then has a very large Dusk rip the jail bars from its hinges and hurl it at her; to the point of cutting a bleeding wound on her cheek. She stares at her incoming death, and keeping her eyes open, prays to Riku and Sora to give her strength and she never backs down.
Later, when she gets her own keyblade; she is much more proficient with it than in the game and rescues Sora from Xigbar later. Xigbar sneers at Sora for needing her help, and Riku states that its fine.