Githyanki brought the tradition of the Bleak Disciple from the Astral Sea. It teaches its adherents to forge the stuff of shadow into a weapon they can useagainst their foes. Its strictest followers keep a white cloth that they dab in the blood of each slain foe, and before they attack a chosen target, they reflect on this memento of the foes they have defeated.
Bleak Disciple: When you hit an unbloodied target, you gain temporary hit points equal to your Constitution modifier. Add 2 to the temporary hit points gained at 11th level and 4 at 21st level.