If you are familiar with bosses, you should know that there are three different kinds of bosses including refined, unique and elite bosses. It means that they will drop refined, unique and elite weapons. Obviously, elite bosses are the best choice because they will also drop some Red stones! If you are lucky enough, the unique bosses will also drop Red stones!
As the map told us, there are 9 different level bosses including 71, 72, 73, 75, 76, 77, 81, 82 and 83. With my experience, I can tell you 71 75 and 81 are refineds, 72 76 and 82 are uniques, 73 77 and 83 are elites! If we wanna gain more, we should have 2 Star-eyes. I advise you to use them to locate 77 and 83. Why? Because 77 is near to 75 and 76, 83 is near to 81 82 and 71. Then take many randoms to search for 72 and 73.
OK, now I will tell you how the bosses refresh. The bosses will refresh in different sequences in different period of time. I am sure there is an invariable sequence: 81→75→76→71→83 →82→73→72→77. After the invariable sequence, it will begin to change. But there is also a rule we can find: Some bosses are related, after you killed anyone of 72 73 77 and 82, one of other 3 bosses is possible to refresh. 72 76 82 and 83 are similar.
Island has many high BP players, so you have to take many randoms to fly to the bosses and avoid the PK. If you are smart enough, I believe you will be the boss king on Island, Good luck!