Probably, each player has killed the dragon, and wants to fight with other bosses. 5 New Bosses Add-on will add 5 different bosses to MCPE 0.17 that have unique abilities. For example, Fire boss has 220 hearts and can infect you special poison. Many bosses can be spawned when you kill certain mobs. Therefore, always keep a weapon and armor and it is desirable some useful potions.
Below you can see all the available bosses. Each has a large number of health and attack in different ways. It is better not to kill the mobs at all if you don’t want to fight with strong opponents.