Dark Figure

Xehanort's Guardian is a special dark entity Xehanort's Heartless, Xehanort himself, and even Riku are able to summon in Kingdom Hearts Birth by Sleep, Kingdom Hearts, Kingdom Hearts: Chain of Memories, and Kingdom Hearts 358/2 Days alike.

Kingdom Hearts Birth by Sleep
After losing to Aqua during their first battle, the new Xehanort became enraged, using the powers of darkness to create the Guardian. He then used this dark entity to re-challenge the Keyblade master. After the battle, the Guardian was destroyed, Xehanort falling into the Realm of Darkness along with it. To save Terra's body, Aqua sacrificed her armor and Keyblade to follow it into the dark realm as well.

Kingdom Hearts
After conversing with Sora over the heart, Xehanort's Heartless proceeded to summon the Guardian, preparing to battle Sora due to his naïvity. It later appeared alongside him during Xehanort's second battle with Sora, again transforming and increasing in size to become part of the World of Chaos. It, along with the rest of the World of Chaos, was destroyed at Sora's hand.

Kingdom Hearts Re: Chain of Memories
Xehanort's Heartless appeared before Riku in Castle Oblivion, enraged when the boy chose to fight rather than submit and allow himself to be possessed again as he had in Kingdom Hearts. He transported Riku to the abyss containing Kingdom Hearts and the Door to Darkness, the Guardian appearing behind him and attempting to attack Riku before the start of Riku's final battle with Xehanort.

Kingdom Hearts 358/2 Days
After realizing his loss to Roxas was inevitable, Riku unleashed the dark power that was Xehanort's Heartless that he had been holding back from within his heart. He gained Xehanort's form, the Guardian grabbing Roxas by the waste and squeezing him to the point of Roxas becoming unconscious. This then allowed Riku to take Roxas to DiZ as assigned, the only downside being the fact that he was stuck in the form of Xehanort's Heartless.

Kingdom Hearts Birth by Sleep
The Guardian will fight for its master, grasping onto Aqua and carrying her high into the air, slamming her against the ground before returning to Xehanort. It may also send electrical surges forward from its fists. As it will do all in its power to prevent Aqua from attacking Xehanort, it may also perform a punching attack to drive her off. It may also fire dark energy balls before vanishing for a time and allowing Xehanort to land a few quick hits with his Keyblade. When the Guardian latches itself onto Aqua, the player must rapidly tap the button to escape a devastating attack. Dodge Roll can be used to avoid many of the Guardian's attacks.

Kingdom Hearts
The Guardian fights this time for Xehanort's Heartless. It will utilize the same tactics as past encounters, also able to fire disks of dark energy from its palms. When Xehanort's Heartless commands the Guardian to "come," it will temporarily defend him from all damage. When it latches onto Sora, a "?" will appear above his head. The Guardian will continue to attack Sora, changing the Attack option to Freeze. If Freeze is selected, it will drain a large portion of HP. When Xehanort's Heartless shouts "Take this!", the Guardian will create an energy shield before Xehanort that damages Sora as Xehanort flies into him. The Guardian also participates in one of Xehanort's most powerful desperation attacks, rising up from the ground several times beneath Sora until the attack ends in a surge of dark energy.

When part of the World of Chaos, the Guardian does no damage to the player, merely creating strong gusts of wind to keep Sora away from Xehanort.

Kingdom Hearts: Chain of Memories
The Guardian will perform the shock attack, punch tactic, and Xehanort's most powerful desperation attack when fighting against Riku. It should be noted that in Kingdom Hearts Re: Chain of Memories, it also can fire the dark energy discs at the opponent.

Appearance
The Guardian has a muscular, humanoid form. Rather than having legs, however, its torso comes to point, where it connects to Xehanort. Its face is partially wrapped in bandages, yellow eyes gleaming above a mouth filled with sharp teeth. A human nose appears in-between these eyes. Two long antennae also spout from the top of the Guardian's head. A hole appears in-between more bandages on the torso in the shape of a heart.

While part of the World of Chaos, the Guardian mutates, its antennae becoming long horns, the rest of its body distorted by the darkness to look more muscular and ominous.