i have an idea, kinda putting this out there without putting a whole lot of thought into it.

have a system where an attack by one player causes a weakness on the mob depending on the position

example: lets say they add musketeer, the musketeer shoots the mob with a skill on the right side of the mob, well now there is a exit wound on the left side of the mob that gives a melee an increases dmg for a few seconds on the left, so you can almost link weopon skills together in a skill chain sort of way but with a unique positioning spin on it.