Sora and his comrades have fought against awesome bosses from many corners of the multiverse.
Alongside Chernabog, there's also Maleficent, Monstro the Whale, and every other hellish spawn of Disney's sinister mind that robbed you of sleep for nights on end as a child. Regardless of how good or boring the boss fight is, you cannot deny that getting vengeance on just about every last one of those bastards was sweet. For example, kicking the godly ass of Hades in Kingdom Hearts II is freaking awesome - mostly because Hades explodes before the fight.
Most of the bosses in the series are some form of awesome. Nostalgic awesome for the Disney villains, "holy crap I feel like a badass" for Those Several Bosses, and just plain cool battles like the aforementioned Dark Thorn and Groundshaker... Every player's going to love at least one.
Also, Chernabog. Disney's Night on Bald Mountain, crap-your-pants scary Chernabog. Set to the original piece by Mussorgsky.
Darkside's first appearance as the first boss of the game. The dramatic music kicks in as Sora turns around to see his shadow rise up- and up, becoming an enormous, tentacle-haired colossus intent on kicking your clown-shod arse. Though it turns out to be an easy boss almost every time you fight it (Chain of Memories excepted), its entrance says very clearly that things are about to get serious. Sadly, the same can't be said for Roxas's own boss, the Twilight Thorn.
An awesome Ascended Fanboy moment goes to one Kurt Zisa of New York, for winning a Square contest "Name-in-Game", and having the Bonus Boss in Agrabah (Kurt Zisa) named after him. And the fight with the actual Kurt Zisa boss is incredible; On one side, Sora and his friends. On the other is Zisa, a giant snake-headed six-armed sword-wielding whirling dervish of a Heartless that can disable your magic, create a shield, chop you up like a blender, and jump on your head in an attempt to squish you. Truly, this is the hardest non-Sephiroth boss in the game.
Sephiroth's fights, especially the one in the colosseum in the original Kingdom Hearts, where there's no weird, Filler plotline between him and Cloud to present it with; he just appears and awesomeness ensues.
Kingdom Hearts: Chain of Memories
As for Chain Of Memories, Captain Hook takes the cake. he uses cards like you, but by that point in the game you'll be used to fighting against card-users. You really have to think strategically, especially during the part where you have to play your cards later or he'll counter yours.
Far better than Hook is the final boss, Marluxia, especially in the PS2 remake, in which he has three stages instead of just two. The first and third stages are particularly awesome.
Zexion is also one of the more creatively destructive bosses in the game, slowly winnowing your card set down and using your own attacks against you.
Pretty much any time you fight an Organization member the second time, especiallyLarxene and Vexen.
Kingdom Hearts II
Xemnas from the first game's Final Mix. With the insanely creepy cutscene prior to the battle, and the awesome music, this battle was absolutely perfect.
Xaldin's boss battle. Sweet revenge...
Also 1st Xemnas, although they're all awesome. Then again, he is the Nobody of the greatest boss ever, Ansem (who has the added bonus of awesome music). World of Chaos is the coolest, but easy.
It's no World Of Chaos, but the battle between Xemnas and his fortress is epic too, taking place inside Kingdom Hearts itself and being the last time you can use Donald and Goofy in the game, thus giving them a chance to go out with a bang.
Really, all the Organization XIII Data battles count. They may be hard, but they are awesome.
The final Xemnas fight in Kingdom Hearts II, when he finally faces off with you in person in the void after a longSequential Boss fight. It culminates with two Keyblade wielders fighting off literally thousands of laser beams!
Despite being an easy boss, the battle against Dark Thorn is strangely awesome. Especially the music.
Same goes for the battle against Groundshaker. You're a tiny (and adorable) lion cub, it's a Heartless so massive it has a freaking tree growing on its back. The only bigger Heartless (so far) is the World of Chaos. Of course you feel like Superman after defeating it. The boss is the size of a freaking mountain. (Shadow of the Colossus, anyone?) And you're fighting this thing with Simba, who has one of the most Bad Ass combo attack with Sora in the whole game.
Sora & Simba:TOGETHER!!
(Sora & Simba proceed to rip everything in the immediate area to shreds)
Another sweet part of the Groundshaker fight is that one of the reaction commands is to get stomped on by his huge-ass foot and, as a tiny lion cub, block the stomp, throw off his foot, then vault into the air to smack it around and knock it out for a bit.
Twilight Thorn was pretty cool too though, especially when he knocks Roxas off the battle platform and into the air, throwing a huge ball of energy at him as he falls.
While not technically a boss fight, it may qualify as the most epic battle for II, if not the entirety of the franchise. On one side: Sora. Alone. On the other: 1,000 Heartless. ONE. THOUSAND. HEARTLESS. And your task? Wipe the floor with them.
Plus, Leon has shown you them at the beginning of the game and at that point, 20 of them could cream you. Now, you fake right, pick up Guardian and give it a keyblade suppository until it vomits a shoop-da-whoop lazor capable of putting you from 0 to 110. Awesome.
The only down point of the 1000 Heartless Battle is that the trailer showed a larger variety of Heartless, including several Behemoth Heartless. If only that had remained...
The Lingering Sentiment is certainly That One Boss, but that doesn't stop him from being insanely awesome. His relentless attacks are all the most unique and powerful attacks in the entire game, and ridiculous amount of health and defense makes it even better when you finally bring him down. And the song, "Rage Awakened", makes the battle even more epic than it already was.
Luxord. He begins the battle by turning you into a die. A die that can't attack, save for a weak body blow, and can't move without using that same move. After you wait that transformation out, your main method of attacking Luxord is accepting his games of chance, Pressing Triangle To Not Turn Into A Card, and using the Action Command that gives you. And even after you've used the games to whittle down his health (or rather, "time." It's a Timed Mission for both you and him, and attacks speed the time up.), he spreads cards all over the floor, turns into one himself, and hides among the pile. For a gimmicky battle, it is kind of fun and exhilarating.
In the second game against Sephiroth, you start by pushing X to not die. Then the fight just gets faster from there. It isn't nearly as hard as the fight against Sephiroth in the first game, but for many gamers, it's much more enjoyable.
Beating Scar in the Pride Lands, kicking the crap out of the guy for killing Mufasa! Lying to Simba! And lying to the whole pride! WHOO!
Bonus points for taking place into the highest point of the Pride Lands with that epic scenery and The Encounter made it even more epic.
Hades. When you finally fight him, he's lost his temper and goes absolutely stark raving mad - and trust me, with THE AWESOMENESS THAT IS JAMES WOODS DOING THAT VOICE IT SOUNDS SO AWESOME! Auron is no longer his puppet, Hercules is over his Heroic BSOD, and now everyone wants to give Hades a piece of their minds. On top of that, their battle is also set to The Encounter. Heck, any Disney boss with this music could qualify for the nostalgia value.
Barbossa, the first Live-Action Disney villain to appear in the series.
Saïx. This complete bastard arranged your girlfriend's kidnapping, has you Kneel Before Him, and then tells you to keep slaughtering Heartless for the Organization's Evil Plan. Taking him on as one of the last surviving Organization members and on the verge of a Villainous Breakdown, fighting this arrogant bastard tooth and nail and then triumphantly finishing him off is extremely satisfying.
Kingdom Hearts: 358/2 Days
The bosses in 358/2 Days are all awesome, with the one absolutely stealing the show being the Infernal Engine. You rush through Beast's Castle, trying to find the unidentified Heartless, when all of a sudden, Beast is freakin' launched over the gates of his castle, landing in the courtyard all battered. This makes you start wondering, 'What the hell could take out the Beast? So, you rush out the gates, and then, Vim and Vigor kicks in, as a gigantic battering ram/siege tower rolls towards the main gates, and from that point on, you're basically reenacting the scene from Return of the King with Grond, if the heroes began viciously attacking it before it could reach the gates. It may be That One Boss to some, but to others, it cemented the game as truly magnificent.
Xion. Pure awesome and the music in final stage is just so indescribable.
Kingdom Hearts: Birth By Sleep
In Birth by Sleep you fight Hades and the Ice Titan at the same time. It bears repeating: Hades and one of the first game's Bonus Bosses. At the same time.
Although you discover after the fight that it's not the Ice Titan but the Ice Colossus, which Hades admits to effectively being a cheap knock-off of the original. It's still an Oh Crap moment for the player before this is revealed.
All Vanitas battles are awesome, though the final one above does take the cake. Coming in close second is Vanitas possessing Ven, in which you fight him as Aqua with King Mickey himself on your side.
The Ventus-Vanitas battle becomes truly awesome when Ventus-Vanitas uses his ultimate attack, which will destroy you if you don't use Mickey's help. "None of this can be changed" indeed.
Terra's Final Boss fight. To clarify: You play the fricking Lingering Sentiment against a Grand Theft Me'd Xehanort in Terra's body! All the while, Rage Awakened is playing in the background. For those who suffered through the Bonus Boss in Final Mix, this is sweet, sweet vindication.
Trinity Armor. Out of the Unversed boss fights, that one was the best; unlike the dumb old Guard Armor from the first game(and it's even stupider Reverse Armor form), it's Unversed counterpart is an actual Mech! Composed of three different Unversed! And a kickass Transformation Sequence! Not to mention it's one of the few boss battles in the game where you get allies for adding coolness; in this case, the OTHER two playable characters(so it's Terra, Ven and Aqua vs. Trinity Armor)! Easily one of the best boss fights in BBS.
The secret bosses of Birth By Sleep qualify as well; Vanitas' Lingering Spirit, while only having one HP bar, is fast and strong; and if you use Cure spells, he does too. Annoying as heck, but an interesting challenge. The Mysterious Figure, first shown in the NA version of BBS, has a bevy of tricks which make him hard as heck, but beating him is sweet indeed. The Final Mix bosses keep up the pace: Armor of the Master(Eraqus' Armor) uses a spell which whips up energy chains to do all kinds of crap, from tying you up, acting as projectiles, and more, has lightning fast combos, and other painful crap. The other new FM boss, No Heart (Xehanort's Keyblade armor, which happens to look a HECK OF a lot like Xemnas' armor, and even has a mix of the Ansem fight music and the final Xemnas fight music as his theme); first he creates a barrier, sitting pretty on his throne while you bash it. After that, he gets off his rear, and kicks your ass with Keyblade combos, hand to hand attacks, dark energy blasts, impaling you with Keyblades....Holy badass.
Either of the encounters with Braig. If nothing else for the awesome music, it shows just how powerful Xigbar was before he was even Xigbar.
The Final Boss. This guy in a Black Coat's been screwing with you all throughout Castle Oblivion, and if you've played Chain of Memories, you're probably expecting Marluxia. You're dead wrong. Cue Moment of Awesome as the man in the black cloak summons Oblivion. And then Oathkeeper. EnterRoxas.
Kingdom Hearts 3D: Dream Drop Distance
Bonus BossJulius. Not only is he hard, not only is he a DisneyBonus Boss, not only does The Encounter play during this fight for the first time on a Nintendohandheld, but he's also one of the fairer secret bosses to recent date in the KH series, being hard because he is legitimately hard, not unfair hard. Quite a refreshing sight after the unfairness that is Vanitas Remnant and Mysterious Figure AKA Young Xehanort, especially the latter.
Young Xehanort, aka The Mysterious Figure from Birth By Sleep. He's fought at the climax as the game's penultimate boss, and as the younger form of the Big Bad, he's a truly vile human being who's effectively responsible for what happened tothe heroes in BBS, as well as Sora's fate in this game. He's fought in an incredibly fierce and agile battle against Riku, the series' resident Badass, so the battle is essentially a Badass vs. a Complete Monster.
Chill Clawbster! You've just seen Monstro swallow Pinocchio and Jiminy Cricket and as you're preparing for a fight, it comes out from nowhere and freezes Monstro alive! What follows is a battle around the frozen Monstro as it flies away from you, smashes down the ice platforms, fires lasers, and is an all-around dick! When you've whittled down its HP, it decides to tuck its tail and flee! What follows is that you must smash a crack on the frozen Monstro to free a part of it, then proceed to Reality Shift and blow bubbles on the freed crack. The result is at the end of the boss fight, you are chasing down Chill Clawbster using - yes, you guessed it, and by god, of all the awesome battles in the series, and there are many, this is by far the most awesome - Monstro the whale!
Xemnas. He is the last boss in Sora's story and you fight him after one hell of a Wham Episode! From the awesome line he spouts at you before the battle starts, to throwing buildings at you (again), to teleporting and floating all around the place, he is one satisfying bastard to beat! At one point, he'll throw a building at the platform you're on, and you have to use Reality Shift to cleave another in two, which allows you time to go completely nuts on him.
Spellican is also awesome for a similar reason- during his boss fight, you get to listen to "The Sorcerer's Apprentice". Not to mention getting payback for that lousy bird summoning all those Dream Eaters in Traverse Town.
Wargoyle, Riku mode. You're approaching the outskirts of town, when this enormous gargoyle comes up and starts shooting at you. It chases you out of town, then heads back to the tower, where you get to fight it. The music, "Majestic Wings", is great, and as much as it's a pain in the ass, escaping the Wargoyle is just plain awesome. Then there's the part where the whole city is lit on fire and you get to ride the heat given off by the flames to attack a giant flying gargoyle with cannons for hands.
The Anti Black Coat. You fight it after a particularly cool Badass Boast from Riku. It's certainly tough and can easily defeat you if you get careless or lack the proper abilities, but the fight is made awesome by the epic and nightmarish music, the shadowy arena, and the bright attacks. You have constantly dash about to prevent the Nightmare's attacks from hitting you. Combined with the eager anticipation of what the story's gonna throw at you next, it's a pretty exhilarating boss fight.