I tried doing this sometime after using this weapon for the first time. Bummed out it doesn't do it. What's the point of the graves that spawn anyway? (Looked up and there is no point)
It is quite simple really. If you get the final swing on a grave you doom stuff. You don't need to hit enemies. It would prob make it busted but think of it this way... you still need to have a grave for this to work. You get them by dooming enemies. It's no where as cheesy as letting serenade kill stuff in its los