Deathblade

This powerful spider venom poison is highly prized by drows for assassination. It destroys the walls of the vascular system causing massive internal bleeding. In a few minutes victims lose blood through all orifices and then die. This poison is made only by drows.
A creature subjected to this poison must make a DC 18 Constitution saving throw, taking 36 (8d8) poison damage on a failed save, or half as much damage on a successful one.