Deathblow

You have become a master of instant death. Starting at level 4, when you attack and hit a creature that is surprised, it must make a Constitution saving throw (DC 8 + your Dexterity modifier + your proficiency bonus). On a failed save, double the damage of your attack against the creature. On a successful save, the target takes no damage, but is stunned until your next turn. The amount of uses increases to 2 at level 7, 3 at level 11, and 4 at level 17.
•You cannot use this ability more than once on the same creature. 
•You must have dagger(s) equipped. 
•You must complete a long rest to use this ability again.