Dual Weapon Mastery

You achieved true mastery in using Two-Weapon Fighting Style, thus gaining the following benefits:

• Increase your Strength or Dexterity by 1, to a maximum of 20. 
• You gain an additional +1 bonus to your AC while you are wielding a separate one-handed melee weapon in each hand.
• You gain two d6 superiority dice to fuel your Whirlwind Attack and can use this attack a number of times equal to your Proficiency Bonus. You regain all of your expended superiority dice when you finish a short or long rest and all uses of Whirlwind Attack after you finish a long rest.

Whirlwind Attack: While you are wielding a separate one-handed melee weapon in each hand, you can use an action to make a Whirlwind Attack. Make an attack roll against each creature of your choice within 5ft of you. On a hit, you can expend a superiority die and add the number rolled to the attack's damage roll. Large or smaller creatures hit by the Whirlwind Attack must make a Strength saving throw (DC Saving Throw: 8 + STR or DEX modifier + Proficiency Bonus). On a failure the creature is pushed 10 feet away from you.