Game:Master Xehanort

Master Xehanort appears as a boss in Kingdom Hearts Birth by Sleep In Terra's story, he fights him three times. The first fight is Master Xehanort and Vanitas fight against Terra, two-on-one. However, the fight is Terra mostly fighting Vanitas with Xehanort standing far off and the fight ended mid way. The second fight (which is also the penultimate fight of Terra's story) is a one-on-one duel between Terra and Xehanort. The third fight is the final fight and you will become the Lingering Sentiment fighting against Xehanort in Terra's body. In Aqua's story, Xehanort will fight her twice in Terra's body in Radiant Garden, the second one with the help of his guardian.

=Terra=

First Battle
Terra will fight both Master Xehanort and Vanitas two-on-one. Vanitas should be the primary target as Xehanort will mostly dodge and keep away from Terra. Vanitas will use his fire ball, lightning, and regular physical attacks here, as well as his typical shadow counter. However he isn't very difficult, and after sustaining minor damage, Xehanort will order Vanitas to attack Ventus and Aqua, leaving Terra to face Xehanort alone. If you wish to speed things along, casting Magnet will stun Vanitas, putting him at Terra's mercy. This fight is merely a warm up for the real fights to come.

Second Battle
The second battle is the true Master Xehanort boss fight. Throughout most of the battle, Xehanort will merely stand around and continually cast spells at Terra. His repertoire includes an array of powerful Thunder, Ice, Earth magic, as well as a quick keyblade combo, all of which have exceptional range, but lack in overall power. The real danger comes from his summoning a number of keyblades in a flowing spiral, and his teleport combo. The former, while relatively easy to avoid, will deal massive damage if hit by it. The latter attack however is more difficult to predict - when the player attacks Xehanort, half of the time he will simply teleport away and attack with magic. On rare occasions however, he will teleport directly behind the player and continually attack with teleport-keyblade combos. A relatively easy fight if the player stocks up on Cure commands, and makes good use of Shoot-Locks.

Third Battle
The third battle is considerably trickier. In this bout, the player takes control of the Lingering Sentiment, while Xehanort himself claims Terra's body and abilities as his own. The real difference in play-style however, is that the player is equipped with the Gaia Bane keychain as a default - all of the previous commands and abilities remain in-tact. Throughout the battle, Xehanort will make frequent use of Terra's own abilities, including Ars Solum, Black Volley, Ultima Cannon, and a powered-up, damage-dealing Sliding Dash, among Xehanort's own abilities such as a meteor barrage and his dark Thunder and Ice magic. The real danger in this fight comes from his frequent use of Ars Solum as his default keyblade combo, as well as the Black Volley Shoot-Lock. Ars Solum is considerably faster and more damaging than in Terra's original form, and the Black Volley is used almost immediately, instead of first locking onto the player. Quick use of the slide dash can easily avoid the Ars Solum, while good timing will perfectly block the Black Volley. When Xehanort is low on HP, he will resort to using a powerful and ranged meteor barrage attack, as well as Terra's Ultima Cannon, albeit once again, without the lock-on. At this stage, the player should make sure they are at full HP, and have a cure ability ready to use. With good preparation, the fight should go down smoothly.

=Aqua=

First Battle
The initial fight is almost exactly similar to Lingering Sentiment's final boss battle in the Keyblade Graveyard, albeit with a condensed moveset. He will mostly use only the Ars Solum and Black Volley attacks, mainly relying on slide dashing behind the player, and attacking with Ars Solum. At this stage of the game, Aqua is considerably more well prepared than Terra, so the initial battle should go down without too much of a problem.

Second Battle
The game's final boss battle is mostly an exercise in repetition, patience, and timing. Xehanort will, 80% of the time, keep his distance and simply have his Guardian continually spam long-ranged attacks for excessive periods of time. There are roughly three ways to break the repetition: Get past the attacks, and deal damage to Xehanort; let the Guardian hit you (an unwise move, considering that all of his attacks deal massive amounts of damage), or simply wait it out until he switches to a different strategy. His attacks will mostly consist of repetitively attacking the player with ground shockwaves, or dark energy balls, all of which do massive amounts of damage. The best way to break the cycle is to make use of the Detonation Square command, luring Xehanort into the damage area. When hit, the player can then quickly run up to him and attack with a full combo, or make use of a powerful command. Eventually, he will switch to his Guardian's signature attack, Dark Shadow, where it continually erupts from the ground beneath Aqua. Simply be patient with this attack, and just avoid it as long as possible - don't risk getting near Xehanort to land a combo. His second attack involves him detaching the Guardian once more to grab a hold of Aqua, where he'll appear in front of the player and attack with a full Ars Solum combo. On rare occasions, he will randomly detach from his Guardian while in the middle of one of its long-ranged attacks, and surprise-attack the player with an Ars Solum. When the player gets Xehanort down to about a bar-and-a-half of his HP, something unique happens: The area transforms into a golden, sparkling dream-like state, with Xehanort reverting back to Terra, albeit stuck in a daze. In this state, the Guardian will be even more vicious with its long-ranged attacks, adamant about keeping the player away from Terra. With quick timing, the player can reach, and will have two options: Either attack Terra with a full combo, and afterward leave Xehanort completely open to yet another combo, or initiate a special attack by hitting square near Terra, and with proper subsequent timing of hitting circle again, both Aqua and Terra will together finish the entire battle right then and there.

Trivia

 * For some reason, Xehanort can transform his Keyblade into Terra's Ultima Cannon even though their Keyblades are different.

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