Seeing as how Vanguard is pretty straight forward, I don't see there being many ways Kai will use the card without us knowing how to do so already. I think it would be more to do with what he would do leading up to the point before summoning and after summoning Chaos Break Dragon. I think what's most terrifying about CBD is it's limit break ability since it's not limited to itself. If Kai's able to soul charge a huge amount, that's going to be real deadly.