I just had a fun idea for duels; Basically, you have a sword, ax, bat, mace, whatever, and it's held directly in front of you, with two hands.
When you swing the mouse and the camera, the weapon you're holding swings with it. If the left mouse button is held down, the faster you swing the weapon, the more damage it does.
In contrast, the right mouse button defends. The more still it's standing the more damage can be defended against. For instance, if a blade is standing/defending perfectly still and the enemy's attack is extremely fast, the damage is nulled to the point it does either very little damage or none at all.
I just thought it'd be cool to have a momentum based fight :D