Seems alright, although I can already hear the whines about using hakanai shouten and formation to get "unbeatable" Dex+Will.
Perhaps if the number of attacks landed was the same, would be less likely to have the opponent decide to flee or whatever(then again, combat locking before that would work, I guess). Personally, I would think that trying to fight something that is basically little more than air, would be a bit of a struggle. Like physical attacks doing less damage(100% physical resistance, like the spirits), but magical attacks burning up the mist a little quicker(100% magical vulnerability or elemental vulnerability).