That One Boss/Role-Playing Game/Kingdom Hearts



This page is about bosses in Kingdom Hearts that give away grief like it's candy. It's rather ironic that a series that's got complaints lodged at it for being easy has a lot of fans raging about difficult bosses...but nevertheless, even some easy games have sudden difficulty spikes.

Kingdom Hearts

 * In the first Kingdom Hearts, it's frequently a toss up between the fight against Dragon Maleficent, and the second battle against Riku in Hollow Bastion, which occur within minutes of each other.
 * The first is massive, taking up most of the space of her battle arena. There are very few safe zones where you can hide from her attacks, and every single one has a huge area of effect. Even her footsteps as she adjusts her aim will generate massive shockwaves in their wake! They all chew through your health like they’re going out of style, especially her flame breath which lingers for several seconds, and her one weak spot (her head) becomes a death trap when she randomly launches her speedy bite attacks or does a 180 spin that leaves her facing the other way. She also has more health bars than any enemy encountered at that point. Only the Final Boss, Hades, , and Bonus Boss Sephiroth have more health. And neither of those have hard-to-avoid Flame Breath that chews through your HP like it's going out of style.
 * The second is technically more fair since he’s a humanoid enemy you can reliably stagger and flinch, but Riku's still a powerful swordsman with a fast, aggressive, yet surprisingly defensive fighting style that will force you to bring your A-Game lest you want to see that game over screen over and over again. And if you’re playing the PS2 original, you don’t want to get a game over because every death means you have to watch the ridiculously long cutscene leading up to the fight. Every single time. And you can't skip it. Many old-school Kingdom Hearts fans have committed every line of dialogue related to the to memory thanks to this hellish exercise in frustration.
 * Some would actually argue Ursula. You fight her twice in quick succession, and both fights are hard. In the first fight, you have a 360-degree combat field (Meaning she can attack you from any angle) and you can't beat or hurt her unless you catch on to her gimmick (throwing magic at her cauldron, something King Triton only vaguely alludes to). The second time, she's a giant who you can’t stun or stagger and is constantly throwing out brutally strong attacks such as blasts of lightning that manifest on top of you and a bite attack that she won't. Stop. Spamming. What really makes these fights hard is the fact that they take place underwater, where you've got clunkier controls and no way to quickly dodge or block her attacks.
 * Stealth Sneak in the Deep Jungle. You fight both him and Clayton at the same time. Now, it would be easy if it were just Clayton, since all he does is shoot from afar and give himself a potion to heal any lost health. However, Stealth Sneak can Hadoken you and summon beams of energy from his eyes if you focus only on Clayton. If you focus only on Stealth Sneak, then Clayton can just snipe your party members with formidable hitscan bullets while Stealth Sneak trounces you. It doesn't help that you learn Cure immediately AFTER this fight, and Potions can't be set to a shortcut. And much like the final Riku fight, dying to this boss is painful since there's a looooong cutscene before it begins. And much like 's speech, many players have Tarzan's horrified declaration of "NOT CLAYTON" committed to memory.
 * If you're playing on Proud Mode, Lock, Shock, and Barrel will kick your teeth in. They zoom and zip all over their playroom so damn fast that you can barely get any hits in, and while you're uselessly flailing your Keyblade around, they're laughing in the face of Mook Chivalry by flattening you with a barrage of attacks that all come out at once. The fact that they're just a bunch of bratty little kids makes losing to them humiliating, and having to haul your ass all the way to back to the top of Oogie Boogie's lair just to fight them again will get old fast.
 * God have mercy on your soul if you're doing a Level 1 challenge, because they are one of its nastiest hurdles. It's not uncommon to die almost the second the fight starts, leaving you staring at a Game Over screen while you try to process what just happened.
 * Cloud is a formidable opponent on his own, and Leon is a lot more dangerous when fighting alongside other people. So when they fight you together during the Hades Cup's 20th seed, they're nearly unstoppable. You've got two powerful boss-level enemies chasing you down and hitting you with powerful sword attacks, some of which can't be blocked, and upon reaching low health they get access to a powerful Desperation Mode to turn the tides on you. God help you if you activate both at the same time.
 * Neverland's secret boss: The Phantom. Merely figuring out how to fight it is a pain, because it takes a page out of Ursula's book by being immune to almost all damage. But unlike with Ursula, the Phantom's weak point must be hit with a specific attack depending on the color, and it can briefly disappear entirely. You're also on a time limit, because Phantom will cast a Doom spell on your party members one by one, signified by a number over their heads that counts down before killing them once it reaches zero. And if they die, that's it. You can't revive or heal them, and can only postpone it by casting Stop/Stopra on the clock tower's hands and freezing them repeatedly. Which, by the way, isn't intuitive or obvious in the slightest. And even when you figure out the trick, you come to a horrifying realization: Stop shares an MP pool with other spells. As in, the spells you need to hurt the Phantom with. Going in without a truckload of ethers/elixirs and you and your party members armed to the teeth with MP-boosting skills is suicide, and even if you're prepared the fight is long, tedious, and a stressful exercise in resource management that will make you wish you were fighting Maleficent or Riku.
 * So you're heading back to Olympus Coliseum to redo the Hades Cup for fun... and suddenly, you notice 2 new challenges among the cups you've previously cleared. Curious, you select the Platinum Match, and are met with an ominously empty, dark arena... until suddenly, a mysterious swordsman with long hair, an even longer sword, and one black wing appears in a flash of light. Final Fantasy VII fans will know exactly who they're dealing with, but newcomers will likely know this guy is bad news just from hearing the opening bars of One-Winged Angel. Say hello to Sephiroth, an utter nightmare of a fight who makes and Final Riku look like chumps.
 * Thanks to his insanely long blade, Sephiroth's standard attacks have a shit-ton of range. So they come out slow to balance things out, right? Ha ha... NO. Sephiroth attacks fast, and he'll combo you into oblivion unless your blocking reflexes are on point. Not content with mere swordplay, Sephiroth's also got some nasty magic attacks that really bring the hurt. Pillars of lava, meteors, and tons upon tons of shadowy balls... However, the scariest tool in Sephiroth's arsenal is Heartless Angel. When you hear him say "Descend, Heartless Angel!" (or alternatively, Sin Harvesting!)? Drop everything you're doing and smack him. Now. Or else you end up losing all of your MP and almost all your HP. All it takes at this point is the slightest poke from his sword to show you that dreaded Game Over screen.
 * The silver lining to this fight is that it's at least a straight-up fight, compared to the Phantom's gimmicky battle. And despite its difficulty, it's nothing compared to the horrific superbosses you'll be fighting in other games further down the line...
 * ...Such as Final Mix's Unknown/. American players more familiar with his boss fight in the sequel's initial release will walk in expecting an easy time, only to get slaughtered by his punishing lightsaber combos and massive electric blasts. He's prone to Teleport Spam, packs some truly scary counterattacks, and fights so aggressively that he makes Sephiroth look like a pacifist. But his most dangerous technique is his "curse", which drains your health and turns the command menu into a sadistic game of roulette where it scrolls between Shock and Release, with Shock damaging you even further if you accidentally pick it. As the series' first Sequel Hook superboss, he provides a very scary look at what's to come in future installments.

Kingdom Hearts: Chain of Memories

 * Riku . You fight him four times over the course of the game, and he's a pain from start to finish. The first fight alone gives him powerful attacks with a ton of range and a tendency to stun you if he traps you in a combo, and he'll start adding tools like sleights and Elixir cards to his arsenal in later fights. This culminates in a truly hellish final battle where he spams sleights with wild abandon, the worst of which being the dreaded Dark Aura, and will keep you from destroying his best cards by using his Enemy Card's effect to keep them in his deck. Even worse, . A lot of fans consider him to be one of the hardest mandatory bosses in the series, and for good reason.
 * In the original GBA game, but not the remake, Captain Hook is far more powerful than the other bosses at that point in the game (the Parasite Cage, Cloud and Hades were nasty as well), partly due to the GBA controls and his stunlock attacks. The field makes that fight in the GBA version even more difficult. As the ship keeps constantly tilting side-to-side, it easily puts you almost always on the receiving end of Hook's bombs.
 * Much like Captain Hook, Dragon Maleficent is a lot harder to deal with in the GBA original than she is in the remake. You've got a lot less room to move around in the tiny GBA arena, and Maleficent's bite and fire breath attacks have a huge area of effect. Her attacks are usually invoked with high-numbered cards, do a lot of damage, and dodging them can be tricky: for instance, her Shockwave Stomp attacks come out blindingly fast, and her fire breath summons columns of flame that appear randomly, meaning you can suddenly lose a decent chunk of health just because one suddenly popped up on top of you. Thankfully, the remake's larger arena makes the fight a lot more manageable, and turns her into a moderately difficult boss instead of a solid brick wall.
 * Despite wielding a shield, Vexen's one of the most aggressive opponents you'll face, and it's rare that you can safely get off a combo on him without swift, brutal retaliation. His tricks of the trade are ice attacks that home in on you and a particularly nasty combo attack that hurts you the second it activates if you're close enough. His sleights are just as nasty: one has him him freeze you solid if you don't roll away at just the right time, another has him summon gigantic ice spikes that are incredibly hard to dodge, and the final one is a series of swings from his shield-turned sword that will cleave off massive chunks of health unless you dodge into them. His plethora of Ethers and Elixirs also make it hard to reliably break his best cards and remove them from his deck, especially if he pops an Air Pirate card beforehand to make those cards impossible to break.
 * He's easily at his worst in the GBA original, because the 2D plane combat took place on meant that he'd nullify any attacks hitting him from the front thanks to his shield. While he can still block your attacks in Re:CoM, it's a lot easier to hurt him since you have more angles to attack him from. (The same goes for the shield-wielding Defenders, who go from by far the nastiest enemies in the GBA game to mildly-annoying enemies that don't even reach Goddamned Bats status.)
 * The fight with Larxene right after the final battle with Riku can be very difficult, only slightly less so than the battle preceding it. Mainly because Larxene is fond of backing you up against a corner and unleashing combo after combo at you when you can't escape. It certainly doesn't help that almost all of her cards are multi-hitting combo attacks.
 * The rematch with Axel near the end of the game is brutal. He's got speed on par with Larxene and will happily cause you to waste cards and sleights with his frequent dodging before punishing you with powerful fire attacks and overly long combos. His sleights are also nearly impossible to dodge unless you have Zero cards on hand to break them, with one near-literally nuking the screen while the other merely sends massive flaming chakrams bouncing around the arena. While he has an elemental weakness to ice that you can exploit, it'll only carry you so far against his aggression and massive health pool.
 * Fittingly for the game's Final Boss, Marluxia pulls out all the stops when you confront him. If you think you're in for an easy time because he's a pink-haired pretty boy that can control cherry blossoms, think again.
 * His first fight is easily the toughest, because he's a hell of a card shark with an answer for everything you'll throw at him. He's got tons of Zero cards to nullify your best sleights, obnoxiously long combo attacks that come out fast, and horrifying sleights such as Deathscythe and Blossom Shower that are nearly impossible to avoid if you can't break them. His scythe gives his attacks a massive amount of range, and his love of Teleport Spam will allow him to nullify hilariously overpowered sleights like Sonic Blade and Lethal Frame on a whim.
 * His second fight is a hilariously easy Anticlimax Boss in the original GBA game and only marginally tougher in the remake, but said remake introduces a third battle that brings its own kind of bullshit to the table. Thanks to being attached to a ghostly grim reaper-looking Nobody, Marluxia technically counts as a monster boss and thus doesn’t have a deck you can remove cards from. However, this does not stop him from using sleights, and when he starts using them he'll spam them to kingdom come. Every single one of them is some flavor of That One Attack, with a few standouts being a whirlwind that scatters your cards around the arena and a series of orbital laser drones that will hound you no matter where you run. But the crown jewel of his terrible arsenal is Doom, a sleight that traps you in a card duel where you’re forced to break six of his cards in six seconds. Fail to do so, and you die. Right on the spot. And there’s nothing you can do about it. While Lethal Frame is a lot more effective here than in the first fight, it won't mean a thing if his sudden sleight spam breaks it, or he hits you with Doom.
 * Zexion can be pretty difficult thanks to his unorthodox fighting style: he steals your cards and creates clones of himself that will use them against you. If you aren't careful, the fight devolves into a total shitshow where you're overwhelmed by a small army of Zexion clones while you can do very little to fight back.
 * Riku’s fight against the Trickmaster is where all the issues players have with Reverse/Rebirth’s Wonderland visit come to a head. Riku uses fixed decks that differ from place to place, and Wonderland's is horrible. You get nine cards total, and none of them have a value higher than five. Trickmaster's attacks can go as high as eight. At best, you're in for a tedious slog. At worst, you'll be humiliated by what should be an unremarkable Warmup Boss thanks to genuinely malevolent game design.

Kingdom Hearts II

 * Despite how Demyx (pictured above) appears to be the Spoony Bard slacker who really doesn't care about anything except playing sitar, you'd be surprised how many people think he fits the description for That One Boss. Sure, there's some Fake Difficulty in the form of Luck-Based Mission in there, which most people don't like, but he certainly isn't one to be taken lightly. To expand upon this, he has a move where he'll summon a few water clones that you have to defeat in a time limit. The catch? You have several seconds to do this, and if you don't succeed, you die. Yep, a game over just for failing at a stupid luck based mission. And to make things worse? Demyx is annoying to fight in general as his attacks have a ludicrously wide range, and they will always blast you into the air as he leaps around the arena like an acrobat (He summons huge jets of water when he jumps).
 * Luxord qualifies as well, simply because of the Unexpected Gameplay Change aspect of fighting him. Instead of just whaling on him until he dies, there's a confusing little minigame that you have to play, the fight is sort of time based, and his card attacks are really annoying.
 * Xigbar also deserves a mention. He is probably harder than Luxord despite being more of a standard boss fight. He teleports all round his arena and blasts you with quick shots from his arrowguns that are hard to avoid. He also can change up the arena into different layouts, making him more annoying to fight. And he has a desperation attack where he traps you in an enclosed area that's very small, and proceeds to bullet spam you to hell. And to note, he's completely invincible while doing this, so there's no way to knock him out of this!
 * Xaldin and his hard to avoid Wind Dragon, though like Xigbar, he's just tough in general. Thanks to his battle style that involves the use of wind and six lances, he hits very hard and fast, and he has ridiculous range in general. Not to mention that the gimmick that gives you an edge in this battle can be clunky and tough to master for first time players.
 * In the Underdrome, Pete is trouble. Being a Time Limit Boss hurts, but the fact he hits like a truck hurts even more. Pete also summons various Heartless and devices which make the fight a pain. If you cannot outdamage him within the proper time, expect to attempt him over and over.

Kingdom Hearts: Birth by Sleep

 * Wheel Master wouldn't be too hard under normal circumstances (and indeed, Ven and Aqua's fight with him in the arena is super easy)... except you fight him as Terra, who's as unwieldy as a pregnant rhinoceros. Wheel Master can easily run circles around him while pelting him with his annoying wheel and spool attacks, and when you get him down to low HP, he'll go on a rampage and furiously charge at you. It's tough to dodge him thanks to the way he homes in on you, and blocking the attack will often result in him simply getting behind you and hitting you anyway. What's especially frustrating is that he's the first boss on Terra’s route, and yet he doesn’t even qualify as a Wake Up Call Boss thanks to most of the bosses that follow being much easier than him.
 * Near the end of his story, Terra fights . The foe is an absolute beast. His attacks are incredibly powerful, and the most dangerous ones come out with no warning whatsoever. Even after you've gotten his pattern down, you have to have the utmost skill to block and/or dodge his attacks, because if you don't, expect three or four hits to kill Terra. Your opponent is also resistant to Dark attacks, and the only Command Style that will activate during this boss is Dark Impulse, so you're at quite the disadvantage.
 * Speaking of Terra's story... Olympus Colosseum. Helmet-less Zack.. When he gets overcharged with Hades' darkness, he's going to let you know what it feels like to be on the receiving end of an Omnislash. It's just as painful as it sounds.
 * , the final boss of Terra's story can quickly turn into this if you don't know the best strategy for him (guard against most of his attacks and use Counter Hammer a lot). He has a combo that is just plain unfair: it involves dropping an unblockable meteor which also causes a bright explosion, and then using Ars Solum twice in a row. It's unblockable when he uses it, but when you do it, he just blocks and Counter Hammers you. Even Terra's ultimate abilities won't do you any good. The developers had the sense to program him with the knowledge of your attacks and how to dodge them. Go ahead. Try using Ars Solum, Meteor Crash, or Chaos Blade. He'll perfectly dodge all of them, then smack you down for even daring to try.
 * Even when he isn't using That One Combo, he'll happily kick your ass with his own overly long standard Keyblade combos that will leave you on death's door, and spam obnoxious charging attacks that allow him to no-sell all your attacks, even your game-breaking mines, mega flares, and shotlocks.
 * And in case you didn't hate him already,
 * Vanitas. Just... Vanitas. It doesn't matter who you're fighting him with, you're in for a rough time. He's an intelligent opponent who's good at dodging your attacks (while smugly taunting you to boot), and any time you land a hit on him, there's a chance of you actually hitting a clone while the real Vanitas drops in from above and cleaves off a huge chunk of health, meaning that you have to rely on hit-and-run tactics since he'll happily punish any combo you commit to. He's also fond of throwing out slow-moving fireballs that split into multiple tiny ones that attack in synch with his own Keyblade attacks, as well as overly long and drawn-out teleporting/charging/keyblade riding attacks that force you to run away from him lest you lose a ton of health. Good luck beating him with Aqua, ESPECIALLY on higher difficulties.
 * Ven's final boss is easily the game's toughest fight against Vanitas (Vanitas Remnant notwithstanding). It’s a three phase gauntlet that starts off like his other fights, where you’re having to deal with overwhelming attacks, obnoxious dodging, and combo punishers, but the third phase throws its own brand of unique bullshit into the mix:.
 * Braig, Xigbar's Somebody. He's got everything you hated about Xigbar ramped up to infinity and beyond: excessive teleporting, huge amounts of burst damage, long periods where you’re forced to run around and dodge layers upon layers of Bullet Hell... and you fight him while playing as the sluggish Terra, and the fragile Aqua. Fun.
 * He's especially bad with Aqua. He's a lot more aggressive while fighting her, and because she's about as good at taking hits as a wet kleenex, failure to block so much as one salvo of bullets will leave you on death's door. He's also packing a few new tricks not seen in his fight against Terra, such as bum-rushing you with zero warning and firing tons of spiky bullets at the ground to serve as damaging traps to cut off your mobility. He also teleports a LOT more, making combo attempts and nice, solid hits with your Commands a wasted effort more often than not.
 * Needless to say, expect entries about how hard some bosses in Aqua's campaign can be -- she requires some practice to master, so part of the difficulty is actually getting used to her.
 * Mimic Master. More HP than the final boss, has a blinding laser attack that he uses very often, (and being blind also takes away your Shotlock!) and when he gets low on health, he creates FIFTEEN clones of you that know every command you do, and they also cast Blackout a lot (again with the blinding!). And you don't fight them all at once; it's 2 at a time.
 * Iron Imprisoner IV. The Iron Imprisoner gets steadily more and more difficult through the first three forms. The third form alone is hard enough, to the point where you can only hope to beat him using shotlocks. The first time you fight this form, it is fairly manageable, but you have to fight him again in order to fight the fourth form, and the second time he's been buffed the hell up. And as for IV himself... His new attacks aren't too bad, but his hammer combo has become utterly devastating, and his fire spin lasts forever. If you slip up and hit square intending to dodge and end up accidentally using your counter, then your combo survival ability gets broken, it WILL be deadly. And then you have to start the arena match over again, which includes several rounds of normal enemies buffed up to hell, not to mention the third form again. Also, if you want to complete the journal, you'll have to do this with all three characters.
 * As a rule, Kingdom Hearts superbosses are balls-to-the-walls insane in their difficulty. Even at their easiest, you’re still fighting something far more difficult than any challenge the main game will throw at you. But there's usually a sense of fairness to them, a method to their madness, if you will. That is not the case for two of Birth by Sleep's superbosses, and they are infamous among the fandom for being utter bullshit with no real sense of rhyme or reason to their fights. The first is Vanitas' Remnant, an incarnation of Vanitas who is so stupidly powerful that he only has one health bar to balance things out. And depleting that is a damn near Sisyphean task thanks to his aggression and evasiveness. You thought it was annoying to have Vanitas dodge or no-sell every other attack? Get ready to rage as he dodges and counters damn near everything you throw at him. You hated how aggressive he was, and how it gave you very little breathing room? We hope you enjoy having none, because he fights like a rabid animal whose attacks let him close the distance in a near-literal blink of an eye. He'll also inflict some truly horrifying status conditions on you, such as reversing your controls or obscuring your vision with darkness, the latter of which makes it impossible to lock onto him and nearly-impossible to keep track of him altogether. Oh, and don't bother healing with Cure magic, because he'll heal away any damage you've dealt to him yourself. Here's hoping you can somehow carve out enough breathing room to pop a Mega Potion when you’re low on health!
 * Funnily enough, Vanitas' Remnant's arena can be his undoing if you exploit the geography. Get behind a boulder and out of his line of sight, and he doesn't quite know what to do and will run around like crazy. Load your Command Deck full of Strike Raids beforehand, and have fun whittling him down by spamming those attacks while he can't fight back. Granted, it's far from an assured victory since breaking his line of sight without dying is tough in and of itself, and him finding you is basically a death sentence. But it's easier than properly fighting him to the point that this hilariously lame and cheap strategy is considered to be by far the best one because he’s just that unfair and overpowered.
 * Even worse than Vanitas’ Remnant is the Mysterious Figure/, a mysterious lightsaber-wielding menace who apes every aspect of Unknown from KH1: Final Mix, save for the ones that would make him a fair fight. There is a lot to cover in regards to how unfair he is, so strap yourself in.
 * He's aggressive. Ridiculously so. He is constantly on your ass and won't give you so much as a second to breathe, and healing will often result in him shredding your health bar down to near-zero a mere second later. Out of his vast arsenal of attacks, only two of them give you the breathing room you need to strategize or heal.
 * Like with BBS's other humanoid bosses, you can forget about landing combos on him because he rarely staggers and can break out of them whenever he feels like it. When he isn't powering through your attacks, he's blocking them with a barrier that converts damage dealt to health restored. And in the case of Mine spells and the almighty Megaflare? He jumps over them.
 * Almost every single attack from him is That One Attack. Highlights include a swarm of drones that home in on you and pelt you with lasers, clones that aggressively hound you while using almost every attack in his arsenal, a fast-moving whirlwind that steals your commands and scatters them, and a fast-falling meteor with a massive blast radius.
 * However, those attacks all pale to a certain one he starts to use late into the fight: Doom. He'll extend a web of energy and if you get caught in it, you have five seconds to wiggle free. Fail to escape, and you're instantly killed, regardless of what abilities you have equipped. Doesn't sound bad at first, except every time you're hit with it, you have a second taken off the clock. And if he hits you with it enough (usually three times), you WILL die because you can't possibly hope to button-mash your way out of it in time. In a way, this attack gives a soft time limit to the battle where you have to hope that you kill him before he can cast it too many times.
 * If you’re playing the original release on PSP, he has another horrifying attack to worry about: Collision Magnet, affectionately dubbed the Rape Rope by series veterans. He’ll transform one of his "lightsabers" into a light whip, and if he ensnares you in it he lifts you into the sky and combos you to death. The attack bypasses abilities that should theoretically protect you from it, and BOY does he love to spam it. People who played the Final Mix/2.5 rerelease got lucky, because they nerfed the hell out of it and funnily enough, made it one of his EASIEST attacks to deal with.
 * Thanks to the random, chaotic nature of his AI, he can chain any of these attacks one after another, often with lethal results. If he, say, blows your commands away and follows up with his laser drones? Or his clones? You're fucked.
 * Halfway into the fight, he turns invisible. You can’t lock on to him, and keeping track of him in the middle of such a frantic battle is incredibly hard to do. At this point, all you can really do is frantically spam Surge attacks and hope for the best.
 * If you’re playing as Terra, this battle goes from being merely ball-bustingly difficult to an outright Luck-Based Mission. Terra's pitiful slide maneuver offers far less invincibility frames than Ven's dodge roll and Aqua's cartwheel, and it can't be chained for infinite invincibility.
 * Despite the robust amount of attacking options given to you by the game's command melding mechanics, most of them are impractical at best or downright useless at worst. He's such an aggressive and oppressive foe that the only commands that will really help you are ones that have a ton of invincibility frames, like Thunder and Fire Surge. And even then, victory is far from assured.

Kingdom Hearts: Dream Drop Distance

 * Were you among the people complaining that Xemnas was too easy in Kingdom Hearts II? Well, complain no more, since it will likely take you some serious level grinding with Sora to get past him in this one! His insanely long and strong combos, as well as the lack of the "Second Chance" ability make sure of that.
 * Being the Mysterious Figure, he is hard. At first, he has, and uses a mix of combo moves. When his HP is depleted, he'll use a time rewind spell, that, if not halted by Reality Shift, basically revives him. Even after using the move, you have to deplete another bnuch of lifebars..while clones of him attack.
 * To round out the Xehanort group, Ansem the Seeker of Darkness is fittingly one hard son of a bitch. The first phase of his fight is tough enough, given how he spams a tough-to-dodge ramming attack that will more than likely trap you in a juggle. But he's manageable if you can survive the initial onslaught, his second phase is MUCH tougher. Due be hiding inside his Guardian, Ansem takes very little damage from your attacks, and all the while his Guardian can nail you with all sorts of nasty moves such as poison spheres, laser discs, and all sorts of assorted nasty attacks. To make things worse, he can blow you and your entire party far away from him, and he's almost always bound to follow up with a hard hitting nasty laser attack that is very hard to predict.
 * And before him, Riku has to deal with the Anti Black Cloak nightmare. It's an all around tough opponent to fight, but it's worst move is easily the one where it drains you down to ONE HIT POINT, making it easy to finish you off with. While it does scatter around your health in the form of HP orbs, it can pick these up itself, and you're basically a sitting duck if you try to avoid it and pick up the orbs.
 * The Spellican boss is an all around pain thanks to packing all sorts of powerful spells (as you'd expect form the name) and the fact that it teleports all over an arena that's very annoying to traverse. But what makes this fight so annoying is that it can lock you in a flowmotion attack where you have to grind after it on a rail while it sends rocks and dark blasts towards you. In a Flowmotion section, you have now way to heal yourself at all, so if you're having trouble getting to Spellican? You're screwed. And to make things worse, it will do this at random later into the fight, which means that you're likely to be dropped in the Flowmotion section with minimal health!
 * Both forms of the Wargoyle boss in La Cite Des Cloches. The melee form Sora fights is very speedy and hits ridiculously hard, and Riku's version flies and spams you to death with fireballs. Combine those with the fact that it summons meteors, and you have one hell of a nasty boss to put up with while you've been dealing with easy ones until this point of the game.

Other Kingdom Hearts

 * Leechgrave in 358/2 Days. It has a lot of HP for that point in the story, hits like a truck, and it doesn't help that there are four regenerating tentacles around that you have to deal with.
 * Also from Days we have the Ruler of the Sky, who is pretty frustrating if you are not ready for him. The fight lasts a long time, and there are some pretty nasty attacks.
 * Pretty much ANY of the bosses in Mission Mode. They all fight identical to their Story Mode counterparts, except with sky-high stats. For example, trying to get past 's second form's Ragnarok spam is pretty much impossible with anybody except Xemnas (who's highly resistant to Nil damage). Unless you're really good at dodging, that is.
 * RE:Coded isn't exactly the hardest KH game to date, but the side-scrolling bosses might give you some nasty surprises on your first few tries. comes to mind. For a "normal" boss, we have, especially its , where it WILL kick your ass within the first ten seconds of the battle over and over.
 * And, of course, the fight against . He's ungodly fast, hits like a truck, can inflict multiple stat effects and even his blocked attacks are very hard to punish. Through the fight, he'll teleport around the arena, fire unblockable, homing light pillars while he dashes at you and attacks and will rain down Frickin' Laser Beams once he Turns Red. For extra sadism, when you're almost finished with him, he'll attack with Frickin' Laser Beams, only to finish the attack and follow up with even bigger laser beams. It gets better: These beams will cripple your DEF stat if it hits. Get hit once, you take ungodly damage. Get hit twice, you die.