It seems to vary lately and so does the amount of damage you do with the same amount of swords. My group has actually been recording and timing things and there are times he is down for almost a full 2 seconds longer than others especially on hard mode. My group hits 3 each run just being safe and we have had damage be down at where it should be for 7 hits and we have seen it do as little as damage of 4 hits. It has even at time made the sound of hitting twice with one swing and the animation stumbles when it happens then you get out to notice the damage isn't where it should be for the number of hits you put on him and that is when this stuff happens. https://www.youtube.com/watch?v=-K_Vm2fUFl8