From Tar Valon Library
Bloodknives are Seanchan assassins, equipped with a ter'angreal in the form of a black stone ring that gives them strength and speed and allows them to blend into shadows. The ter'angreal is activated by touching a drop of the wearer's blood to it after which it leaches the life from them. Removing it can slow the process, but once started, it is irreversible. This process will ultimately kill the wearer. They wear black leather with no cloak or helm and three knives at their belt. When going on a mission, a ritual is performed first, the person sending them kissing them lightly on their forehead then laying their fingers on the spot and saying the words "May your death bring victory, may your knife draw blood. May your children sing your praises until the final dawn" (TGS, Ch. 36).
Tuon sends a company of five in the raid on the White Tower (ACoS, Ch. 37). One is killed by Gareth Bryne. His years of experience and the bond awareness allowed him to respond, whereas Siuan did not even see him. In the process, the assassin is able to touch Bryne, poisoning him with a tiny black pin. Siuan has to Heal him (TGS, Ch. 41). The location of the other four is unknown.
Egwene is the intended victim of four Bloodknives; she mistakes attempts to be of Mesaana's doing and plans to lay a trap for her. This fails, as Gawyn scares the assassins off, by appearing at Egwene's door. Gawyn leaves for Caemlyn. In Caemlyn Gawyn finds out more about Bloodknives through Marille. But she cannot tell him more than that they are assassins sent by the Empress and die only when “their blood turns against them.” Kaisea tells him about the Bloodknife ter'angreal rings and that a Bloodknife’s blood is poisoned through the use of the ter’angreal. (ToM, Ch. 33) On a night during which Egwene is battling Black Sisters in Tel'aran'rhiod the Bloodknives set a trap for her and plan to kill her. Luckily Gawyn returns and manages to kill them, but is stabbed in the process. Egwene wakes and heals him.
Afterwards Gawyn, who knows about the Bloodknife Ter'angreal, takes all three rings and puts them in his pocket. (ToM, Ch. 38)
Marille upon seeing Gawyn with a Bloodknife in Caemlyn: “You did not win it in battle, because men do not defeat Bloodknives. They are unstoppable. They only fall when their own blood turns against them.” (Marille to Gawyn, Towers of Midnight, Chapter 33)
Marille: “Shrouded in the night, sent by the Empress’s will – may she live forever – to strike down her foes in her name and glory.” (Marille to Gawyn, Towers of Midnight, Chapter 33)
“Before they die, they will see their duty fulfilled.” (Kaisea to Gawyn, Towers of Midnight, Chapter 33)