The most important thing for this event is the last hit. The rule that the one who kills the monster is basically a rule that enforces kill stealing. Even though some of the players did not want to but they will need to resort to that tactic if need be.
Kill Stealing or KS for the acronym is a very popular term in the gaming world. It is either very fun or very annoying depending on which side the player is on. The ones benefitting for kill stealing will definitely rejoice be it monster or player. They gain the points of the others with minimal effort just because they managed to hit it last.
For the one being the victim of kill stealing, let us just say that some keyboards and monitors did not survive back in the day. For Pandemonium, there are even players that quit after they got their kill stolen by another player, but they soon came back after a week or so. The thrill of Pandemonium is not that easy to keep away.