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.

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 out of harm's way. In the second fight, Sora fights him alone. Ansem uses two new attacks: one resembles Dark Aura, 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. During this time, Ansem is invincible, and the attack must be avoided either by running or by using Dodge Roll.

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 Rockshatter (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 Rockshatter, but Dark Shadow can be avoided easily by dodging.