In the Imperium, psykers are feared not only for their strange powers but for the untold harm which can and often does arise when their powers are used carelessly. When the abilities of a psychically-active mind are wielded by those weak in faith or will, the psychic energy can congeal within the fabric of the Warp to form Astral Spectres. These malevolent shadow creatures attack humans and devour their soul–essence to replenish the psychic energy from which the Spectres were born.