Enigma Heartless are enemies appearing in Kingdom Hearts: Sorrowful Echoes.
Seeking all the memories in the universe, the Enigma Heartless attacked and consumed several worlds. Sensing that there may be another Keyblade wielder, they tried to destroy him and his homeworld.
The means by which Enigma Heartless are created is never explained in the game. They share characteristics with both Pureblood Heartless: in that they themselves lack an emblem and do not release hearts when destroyed, and Emblem Heartless: in that they come in a wide variety of forms.
Enigma Heartless rarely seek out hearts, unless provoked. They show more interest in the memories, thoughts, and knowledge of people, especially those involving the Keyblade. Later in the game, it is revealed that their purpose is to destroy any remnants of the Keyblades, thus preventing anybody from fighting back.