Soultrace

When a being of sufficient spiritual power, be it a person, beast, plant, or something else, has passed from this world, they leave behind an echo of their spirit. This power coalesces into a vague approximation of the form it held in life, composed of essence given sentience. This spiritual remnant is referred to as a Soultrace, or more informally, a Dreg. Legend has it that one can bind themselves to a Soultrace to gain its power.
There are a few materials (namely adamantium and silver) that are particularly effective as weapons against constructs, Soultraces and similar beings. To a lesser degree they can also hamper Weavers, as these materials disrupt the flow of essence through Soulthreads. Against a creature like a Soultrace that is entirely made of essence, silver can disrupt their form much more easily than normal weapons.