This plugin is made for generating mobs (we'll call it "bosses" afterwards) that are designed for players to battle with. Mostly used in RPG servers. You can use it to generate them in wanted time periods and you can change their nbts, potion effects, drops and the locations to generate in the config.yml. Make sure the chunk the boss is at is loaded in order to let the plugin reset the boss when executing the activate command. /forceload is a nice choice.