The Dying Worlds are filled with Thralls. They are basically the souls of fallen warriors and craftsmen, left behind and awaiting judgement before they can move on to the afterlife.
If players capture a Thrall, they can shortcut the crafting process and bind them into their items.
If players bind a Thrall into their item, the properties of the item change in certain ways. Example: a Smith’s Hammer that has the trapped soul of a Dwarven Forgemaster bound within it, and that his skill and life experience is being used to make that hammer stronger and more precise with every swing.