Dagger of Venom

Source: D&D 5.2 SRD Magic Items

Weapon (Dagger), Rare

You gain a +1 bonus to attack rolls and damage rolls made with this magic weapon.

You can take a Bonus Action to magically coat the blade with poison. The poison remains for 1 minute or until an attack using this weapon hits a creature. That creature must succeed on a DC 15 Constitution saving throw or take 2d10 Poison damage and have the Poisoned condition for 1 minute. The weapon can't be used this way again until the next dawn.