I hope that this is not the sole factor as to increase/decrease the difficulty of each open world boss and their minions. There are several factors that affect the burn rate and eventually KO the boss. 1) Number of DPS vs support roles (Tank, Controller, Healers). If a significant number of players in the zone are DPS, then the success rate would be much higher than a group of say half DPS and half support. 2) The real level of each player in the zone. Since you allow CR-15 level players to participate, lets take this into account. A CR-15 player will do significantly less damage than an end-level player. So if you have a group of say 30-40 CR-15 players, and only use the number of players to increase the difficulty, then they probably will not be able to KO the boss. I have seen a group of 15 end-level players KO the bosses. I have been in both types of groups and have seen a huge difference in the success rate. 3) Are you preventing controllers from debuffing the bosses and minions? This affects the effectiveness of the overall damage from the players. Hopefully, the devs will take these other factors into account when calculating Boss difficulty. At the moment, it seems to be just the number of players. What can we expect to be a minimal successful group size, composition, CR level, that would be successful in completing all of the bosses (including hydra)?