Improved Great Weapon Master

You've learned to put the weight of a weapon to your advantage, letting its momentum empower your strikes. You gain the following benefits:

• On your turn, when you score a critical hit with a melee weapon or reduce a creature to 0 hit points, you can make one melee weapon attack as a free action. This ability can stack to maximum of 5 times in 1 round no more, this includes reactionary attacks.
• Melee attacks made with a heavy weapon that you are proficient with deal an extra +10 to the attack's damage. no penalty to your attack.

This ability nullifies the Original Great Weapons master feat