Darkling

The Black Costume is a Pureblood Heartless that appears in Kingdom Hearts χ.

Born from Keyblade wielders who succumb to the darkness in their hearts, these Heartless retain the ability to speak and access the Lanes between, but unlike their human forms, they do not draw power from the Book of Prophecies' fragments during battle.

Story
Outside the clock tower in Daybreak Town, the Player and Skuld are attacked by a group of Black Costumes. The Heartless demand the Keyblade wielders give them their captured Lux, but they flee after a Nightmare Chirithy appears before them.