Kingdom Hearts is one of the best Square Enix RPGs of all time. Combining their properties with Disney's, it was a wonderful game with some great bosses to fight.

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Though there are many bosses in the main campaign, there are also some optional bosses that can be fought if players are looking for more challenges. While some of these optional bosses can be fought during the main story, others aren't unlocked until beating the game, including Kingdom Hearts' most iconic secret bosses. Here are the most difficult optional bosses in the iconic RPG.

16 Guard Armor Teamed Up With Blue Rhapsody And Red Nocturne In The Hades Cup

Sora, Donald,, and Goofy fight Guard Armor

Guard Armor is a boss that players need to fight early in the game. In fact, it's the first boss in which Donald and Goofy join the party. It can be fought again multiple times throughout Sora's journey. One time where the boss is optional is during the Hades Cup, one of the tournaments in Olympus Coliseum. It is joined by two Bleu Rhapsody and Red Nocturne Heartless in the 37th seed.

15 Leon And Yuffie Fight Together In The Pegasus Cup

Sora, Donald, and Goofy fight Leon and Yuffie

Leon and Yuffie are two of the most popular Final Fantasy characters that became Sora's friends in the game. But that doesn't mean that players can't fight them. In the Pegasus Cup, a tournament that players can compete in prior to unlocking the Hades Cup, they prove how well they work together in the last seed.

14 Destroyed Behemoth Is A Boss In The 40th Seed

Kingdom Hearts Destroyed Behemoth

Behemoth is a powerful mini-boss that players will run into several times towards the end of the campaign. However, an even stronger version of it, Destroyed Behemoth, can be fought outside of the main story. Players can battle it in the 40th seed of the Hades Cup.

13 Hercules Can Be Fought In The Last Seed Of His Cup

Hercules in Kingdom Hearts

Similar to Leon and Yuffie, Hercules is a friend of Sora's that players can fight in one of Olympus Coliseum's tournaments. In fact, he has his own Cup named after him. In it, Hercules proves how strong he is to his junior hero friends in the last seed.

12 Cloud Is Tougher In The Hercules Cup

Cloud in Kingdom Hearts

Cloud is the main protagonist of Final Fantasy VII. In Kingdom Hearts, he was a mini-boss that players could fight against at the beginning of the game. Afterwards, he became friends with Sora, but ended up competing against him again in the Hercules Cup. In the fourth seed of it, Cloud proved just how strong he could be.

11 Yuffie Fights Alone In The Hades Cup

Yuffie Hades Cup boss battle

While Yuffie was already tough to beat when she was with Leon in the Pegasus Cup, she proves to be even more powerful in the Hades Cup.

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Though she fights alone this time around, players are faced with a greater challenge in the Hades Cup's 44th seed.

10 Cerberus Strikes Again In The Hades Cup

Sora, Donald, and Goofy fight Cerberus

Like Guard Armor, Cerberus is a boss that players can fight in the first few hours of the game's campaign and returns in the Hades Cup. Players can fight him in the tournament's 30th seed.

9 Opposite Armor Fights With Six Darkballs In The Hades Cup

Opposite Armor Kingdom Hearts

In the 24th seed of the Hades Cup, players can fight Opposite Armor again, who they had to beat when Sora, Donald, and Goofy returned to Traverse Town. Though the Darkballs that it fights alongside with aren't much of a threat, Opposite Armor is a more powerful version of Guard Armor that shows its true strength in this battle.

8 Rock Titan Is The Last Boss That Players Fight In The Hades Cup

Rock Titan Kingdom Hearts

The Rock Titan is the last boss that players need to fight in the Hades Cup, but that doesn't make it the hardest to beat. As the weakest of Hades' Titans in the series, Rock Titan gives players a small taste of how strong its comrades are.

7 Cloud And Leon Join Forces In The Hades Cup

Cloud and Leon back to back

There are a few mini-bosses in Kingdom Hearts' campaign where the story progresses no matter if players defeat them or not. Leon and Cloud are two of them, and they team up in the 20th seed of the Hades Cup. Fighting these two iconic Final Fantasy protagonists was a great treat for Square Enix fans.

6 Ice Titan Can Be Fought In The Gold Match

Sora vs Ice Titan

The Ice Titan is a boss that players fight in Olympus Coliseum, but isn't part of any tournament, but rather the Gold Match. Players will have to beat the Hades Cup before unlocking the Gold Match, where Ice Titan proves to be a huge threat, and much more powerful than the Rock Titan.

5 Hades Is The Strongest Boss In His Own Cup

Hades in Kingdom Hearts

Despite being an optional boss, Hades was one of the main antagonists of the, working with other iconic Disney villains to defeat the heroes.

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Players are able to fight him in the 10th seed of his Cup, where he finally shows how strong he can be. He has some very powerful attacks and is able to temporarily stop players from dealing damage to him.

4 Kurt Zisa Is A Difficult Boss In Agrabah

Kurt Zisa

Kurt Zisa is one of the challenging secret bosses that players can fight at the end of the game. In order to find Kurt Zisa, players have to go to Agrabah and ride on the Magic Carpet. In a cutscene, Kurt Zisa will attack, beginning one of the toughest battles in the game.

3 Phantom Is A Challenging Secret Boss In Neverland

Sora vs Phantom

Phantom is another secret boss. In order to fight it, players need to go to Neverland and speak with Tinker Bell. She brings Sora and his party to the Clock Tower, where players meet the Phantom. This battle requires players to use magic a lot so they should have as much MP as they can.

2 Sephiroth Can Be Fought In The Platinum Match

Sephiroth vs Sora

Sephiroth, the One-Winged Angel, is arguably Square Enix's most iconic antagonist, first appearing in Final Fantasy VII. However, players can also fight him in Kingdom Hearts. He can be found in Olympus Coliseum's Platinum Match and is one of the most powerful bosses in the entire series.

1 Unknown Is The Toughest Boss In The Game

Unknown KH

Unknown is the only boss in the game that is stronger than the One-Winged Angel. Players can fight him in Hollow Bastion, where they fought Maleficent's dragon form in the main story. Unknown is the toughest boss in the entire game to beat. Eventually, it would be revealed that he is Xemnas, the leader of Organization XIII, who fans fight throughout the series multiple times.

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