Crowfall introduces Thralls in the upcoming War of the Gods update
Crowfall's latest dev diary introduces Thralls which are coming in the next update, War of the Gods.
Thralls have a ghostly appearance that visually sets them apart from the Eternal Crows. Thralls are the souls of fallen warriors and craftsmen, spirits who cannot leave the mortal plane and move into the afterlife. It is a common belief that they are connected in some way to the Hunger, the mysterious force that is corrupting the universe, destroying the Dying Worlds and the creatures who inhabit them.
Thralls will only appear at night time in Hunger-infested areas, come morning they will not be visible. These thralls will be the only source of soul essence and soul gems which are required for crafting the best quality Discipline Runestones which are needed for crafting higher quality Major Disciplines.
Thralls can be found as minions or bosses, with the later giving the best resources and only found in Campaign Worlds. Different Thrall bosses will carry specific soul gems which are used to craft different Major Disciplines.
You can read about all this in full detail on the official site.