Lethal Assassin (5e Feat)
From D&D Wiki
You are a master in the art of killing. You gain the following benefits:
- Once per turn, you can deal an extra 1d6 damage to one creature you hit with an attack if you have advantage on the attack roll. The attack must use a finesse weapon.
- When you hit a creature that is surprised with a finesse or light weapon, the hit is a critical one.
- You gain proficiency with the poisoner's kit. If you already has proficiency, you can add the double of your proficiency bonus in checks made with it.