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There are four hidden bosses in Kingdom Hearts. One gives you a very useful magic spell, while the other three are for prestige only. You can fight the first one by visiting Tinkerbell in the Ship's Cabin after finishing Neverland. This guy, simply called Phantom, has a Death Sentence-like spell that kills off your party after a certain amount of time-cast Stop on a clock face to delay it temporarily. To hurt the boss, note his current color: cast Thunder if yellow, Fire if red, Blizzard if blue, and use regular physical attacks if he's anything else. Beating him earns you Stopga, which will likely be your last "ga" spell. Once you've got them all, Donald gets one more rod weapon. The other three optional bosses are all exclusive to the U.S. version of Kingdom Hearts. Beating them takes extreme patience-don't expect to put a dent in any of them until you're at least level 60. The first one, Sephiroth, is unlocked by finishing the Hercules Cup in the Olympus Coliseum. He's essentially a staggeringly powerful version of Cloud...with a dash of scathing magic on the side. Equip Second Chance, keep Aero on at all times, and use every offensive ability in the book. When in doubt, level up some more. You can fight the Ice Titan after finishing the Hades Cup. His only vulnerable spot is his face, and the only way you can hit it is by blocking the ice shards he throws at you, deflecting them back upward. It's not nearly as difficult as it looks, making this battle a great way to stock up on experience if you're aiming for level 99. Finally, Kurt Zisa can be accessed by going to Aladdin's House after finishing Hollow Bastion and talking to his carpet. Kurt has two forms: one where he throws slashing blades at you and another where he floats around in a bubble and drops stationary fireballs. The first form's the worst-keep moving at all times to avoid getting hit-but the second one's easy if you can make him run into the fireballs he throws out.