So basically I've noticed that many exaggerated weapons such as axes and hammers are cool looking or rather intimidating but are unwieldy. Even if the wielder supposedly has super strength it does not sound like an acceptable excuse.
Lets say a very skilled craftsman wanted to create such a weapon, for arguments sake lets make it a very exaggerated halberd. What method could be used to shift the weapons balance, making it more balanced when spinning it around and unbalanced to put more force behind a strike? The level of technology is medieval but said craftsman has more knowledge of metals and their properties as well as being precise enough to carve minute mechanisms.