Can someone clarify for me? Since the previous update where they upgrade the treasure chests based on the NMs being killed...

Does the player have to be involved in their defeat? Or does everyone get rewarded when someone defeats them?

I've never even seen one of these mobs, and now they're adding the bosses via this same method. Assuming that they spawn for the given world server to defeat and it doesn't matter if individual players participate.... why did they do it like this? Don't they think people want to batle these bosses again? Why would you make them world spawns when they were BCNMs before? Even if everyone gets rewarded, people will miss out on battle content.