Game:Ansem, Seeker of Darkness

Xehanort's Heartless is a boss in Kingdom Hearts and Kingdom Hearts: Chain of Memories. He is fought twice in both games under the name "Ansem".

Kingdom Hearts
Sora, Donald, and Goofy fight him in End of the World. He is fought alongside his Guardian Heartless. In battle, he shoots energy disks resembling Strike Raid, uses his Guardian to attack physically, and sends his Guardian to possess Sora while he creates an energy shield around himself that deals damage. Usually, this can be avoided, as Ansem yells, "Submit!" before doing this, and Sora can glide or even Superglide out of harm's way. However, in the event when Sora is possessed by the Guardian, the Attack command will occasionally change to Freeze for the Guardian to hold Sora in place while Ansem does damage to him. It is best to physically attack Ansem while within reach, and heal periodically, because while in possession of Sora, the Guardian will reduce Sora's HP. Alternatively, you may stay out of Ansem's reach and then hit the Freeze command - Sora will just be held in place while Ansem will be too far away to deal any damage to him. Also, this prevents Sora from losing any HP.

In the second fight, Sora fights him alone. Ansem uses two new attacks: one resembles Sonic Blade, in which he shoots back and forth across the arena. This can be blocked using Guard or Aero. The second has him sending Guardian into the ground, creating dark pools underneath Sora which the Guardian shoots out of with its fist raised (indicated by the line "My strength returns"). During this time, Ansem is invincible, and the attack must be avoided either by running, Supergliding or by using Dodge Roll. Failing to evade this attack can be highly damaging or fatal, depending on the amount of HP Sora has. He still uses his Guardian to possess Sora. As in the first battle, stay out of harm's way by Gliding or Supergliding. However, if Sora is possessed, you have two options: attack Ansem periodically and heal when necessary (as the Guardian reduces Sora's HP), or stay out of Ansem's way and activate the Freeze command for the Guardian to hold Sora in place, so that nothing will be done to lower Sora's HP count.

The third and final fight with Ansem involves the World of Chaos - see World of Chaos for more strategy information.

Kingdom Hearts: Chain of Memories
Riku fights Ansem twice in this game. The first time, Ansem shoots out a bolt of lightning that travels horizontally. This can avoided by jumping or dodging. Ansem's only other attack during this first fight is a weak physical attack using Guardian. The second time Ansem is fought is during the Final Battle of Riku's Story. This time around, Ansem brings into play some of his attacks from the first game, such as the Sleights Dark Rush (where he zooms back and forth across the arena) and Dark Shadow (when he sends his Guardian into the floor, creating pools of darkness that the Guardian rises out of, fist raised). It's best to use zero cards to break Dark Rush (Although it can be jumped over with perfect timing in CoM), but Dark Shadow can be avoided easily by dodging.

In Re:Chain of Memories, note that Ansem still uses his Strike Raid-like attack during the final battle - Riku can either break this attack or dodge it.