Great Weapon Adept

You've mastered the art of using a weapon's weight to your advantage by using its momentum to strengthen your attacks. You gain the following benefits:

Once on each of your turns when you score a critical hit with a melee weapon or reduce a creature to 0 hit points with one, you can immediately make one melee weapon attack (no action required).

 Before you make a melee attack with a heavy weapon that you are proficient with, you can choose to take a -5 penalty to the attack roll. If the attack hits, you add +10 to the attack's damage. You cannot do so if the attack is made with the opposite end of your weapon.