Ouroboros Rapier

You gain a +1 bonus to attack and damage rolls you make with this magic weapon. Whenever you roll an 8 on the damage die for an attack made with this weapon, the target of the attack takes an extra 1d8 poison damage. In addition, when you roll a 20 on an attack roll with this weapon against a creature, that creature must make a DC 15 Constitution saving throw. On a failed save, the creature takes 3d6 poison damage and is poisoned for 1 minute. On a success, the poison damage is halved and the creature is not poisoned.