We all know that kaido is said to be the strongest creature on land,air and water. Based on what we know so far I'd like to make some weakness analysis. Spoiler From chapter 923 early scans its easy to say luffy's gear 4 barrage didn't even make a dent on kaido and the fact that he is a mythical zoan means there is a special trait for him(for example marco has healing power aside from increased strength and agility)My guess is that kaido's special trait makes him very endurable ,gives him inhuman stamina and makes his outer skin even without haki , harder than advanced armament haki .So to cut it,one would require some serious blade skills .Kaido is the strongest creature on water despite having a devil fruit ,I simply don't know how but if that was an overstatement then sea water or that water stone (i think kairousuke) smoker has in his sword-stick thing could possibly be included as one. Possible Weaknesses: ->We've seen kaido drink and he got high which proves that his body inside acts in a normal way,so one of his weaknesses might be poison ,other devil fruit or some kind of tranquilizing liquid..etc ->Kaido cried on hearing Doflamingo's capture which implies that he is mentally sensitive.Also he is extremely reactive to someone hurting his ego or pride,as we saw him send two of his underlings flying away when they mentioned that he shouldn't take law and luffy lightly.So in battle strategic guys can use this and bait kaido like waving a red cloth infront of a raging bull. ->From the introduction of kaido it is clear that kaido is unkillable but not undefeatable,by exploiting any of the above weaknesses one can gain an edge on a battle with kaido. ->Also one final thing I think would be used against kaido is if law takes his heart out while he is busy battling they could literally own kaido(Although this seems too easy and would never happen ). ->Since Kaido's level of haki is not known it is not clear how much a haki master would fare against kaido.This is the reason i did'nt include any haki related exploits. P.S: The weaknesses I put are pure speculations,if you have any other ideas feel free to post them.