Blade of Vengeance

When a creature makes a melee attack against you and misses you can use your reaction to make a counter attack. You can take a -5 to the counterattacks roll to add +10 to the rolls damage. You must be proficient with the weapon you are wielding. You may only do this when an attack roll misses. This feat does not work for attacks that hit. 

Note: You don't have to take the -5 to your attack roll. You have the choice to make a regular attack roll instead, However you MUST have Great Weapon Master, or a similar feat that gives Mastery of your Chosen Weapon Type before you can take this Feat.