Hunk of Iron (Greatsword +2)

This blade was commissioned by a king to a fledgling blacksmith. When completed, the king deemed it far too large, and refused to pay for it. Even the blacksmith who forged it had to admit that it was too big, too thick, too heavy and too rough. It was more like a large hunk of iron...
This colossal weapon sunders armor to pieces. Enemies critically hit by this weapon suffer a permanent -1 to AC. Furthermore, its titanic weight causes creatures hit by it take an additional 1d8 bludgeoning dmg.