The Flay artifact was a projectile weapon wielded by Kain as a fledgling vampire during the events of Blood Omen: Legacy of Kain. When hurled the Flay would seek out and kill an enemy in a bloody explosion; ripping the flesh from the body and leaving behind nothing but a blood-stained skeleton. Although the Flay is described and functions as an energy based projectile it is also depicted as a metallic throwing weapon.
Following the events of Blood Omen the Flay in never seen or mentioned again. According to Daniel Cabuco, Kain in Soul Reaver can passively use Flay, similar to what happens with Beguile in Blood Omen 2.
"Kain had lightning and a teleportation ability, which for gameplay purposes in Defiance, we turned into the mist form. Kain had a whole host of spells from Blood Omen that I wanted to kind of re-do for the next game (flay for example)."