The Hades Cup is a series of arena matches at the Olympus Coliseum that becomes available after winning all prior cups and sealing the Final Keyhole at Hollow Bastion in Kingdom Hearts and its Final Mix version. It is by far the hardest and most dangerous cup in the game, featuring 49 seeds of every enemy encountered in the game, excluding those from Atlantica and several unique to Final Mix. For each boss defeated at the tenth seeds you are allowed to restart the Cup from that seed onwards, effectively saving you a lot of time if you fail partway through.
The 44th seed will be against Yuffie, who will not pose too much trouble alone, and grants the Genji Shield for Goofy upon her defeat. The boss on the 40th seed is a Destroyed Behemoth (a normal Behemoth in the original version). You receive Blizzaga upon victory. In the 37th seed you encounter the Red Armor enemy, the separate parts of which you fought in the Phil Cup. The 34th seed includes a Sneak Army, a weaker variant of the Stealth Sneak boss. The boss of the 30th seed is Cerberus, whom also has no new moves. With High Jump you can get onto his back if you wish. Defeating him grants you the Thundaga spell.
In the 24th seed you face the Opposite Armor, followed by both Cloud and Leon in the 20th seed bossfight. Both of them have been fought before, and you primarily have to focus on one while avoiding the other. This fight does remain one of the toughest solely due to their quick attacks and high damage output however. Winning will earn you the Lionheart Keyblade, which is one of the best Keyblades available. The final nineteen rounds contain the toughest Heartless, in particular those from Hollow Bastion and End of the World. Hades himself is fought at the 10th seed.
Hades solely uses fire-based attacks, making accessories (such as the Ifrit Belt) that improves your fire resistance quite effective. He also has several clear quotes preceding his attacks, making it easier to predict what he will do. Relying on Curaga and Aeroga is recommended as usual. Hades will start with a flamethrower attack, when he says "Take that!", and begin to follow you around. You can either avoid it by running away, or cancel it entirely with a well-aimed Blizzaga. Hitting him from behind also works if he goes after one of your allies (which he is prone to, if they attack him).
When he says "Feel the heat!" he will become invincible, move to the center position, and summon horizontal pillars of flames from his arms. He will then rotate around, forcing you to either keep up with the flames, or stick to the edges of the arena where they can't reach. Alternatively you can Dodge Roll through them, but sticking to him closely will be enough as well. Afterwards he resorts to melee slashes and throwing fireballs, the latter of which can be deflected to stun him. Aeroga will do so automatically, which is rather convenient. After enough damage has been dealt his flames will turn back to blue again at which point the cycle repeats.
Other than these moves he can also hit you from a distance with a burst of fire, which cannot be blocked, only evaded. He has little defense against a continuous melee onslaught other than repeatedly floating away from you. Defeating him grants you the Graviga spell, as well as Ansem's Report 8.
The fifth, third, and second seeds all feature too many enemies to be fought at once, and will simply keep spawning them until the total number has been defeated, making them among the hardest in the entire cup, primarily due to the war of attrition at that point. The final boss for the Hades Cup is the Rock Titan.
Rock Titan bossfight
Despite being the 1st seed's boss, Rock Titan is incredibly easy. Start by attacking its feet, which it can use to cause large shockwaves. Although they are only deadly if you let them step on you. Eventually it will fall over, allowing you to climb up on its body and start dealing direct damage to its heads. The heads only can attack by smashing up down, which is easy to avoid by attacking from the sides, and switching to the other head if one attacks. Lastly it will sometimes smash both its hands onto the floor, creating a massive shockwave that also deals a lot of damage, but it is slow and easy to see coming and thus easy to avoid.
Completion of the Cup grants Trinity Limit, and access to the solo and time trial challenges. Completing each respectively rewards you with the Save the Queen and Save the King weapons, some of the most powerful weapons for Donald and Goofy. Due to the cup's length the time trial lasts twenty minutes, although both it and the solo challenges likely cannot be attempted haphazardly, especially on Proud difficulty.
After the Hades Cup the Gold Match also becomes available.