Possessor

The Possessor is the first Heartless boss from Kingdom Hearts II.

The Possessor worked with the Thresholder's Heartless to defeat Sora in Beast's Castle. After being forced out of its body, it floated about helplessly before returning to the door, bringing the Thresholder back to life. Sora could not defeat the Thresholder until the Possessor was drained of life force, after which it disintegrated.

Gargoyle Knight or Gargoyle Soldier, upon defeat, release globs of darkness that look similar to the Possessor.