Within the game, regarding PvE within Dragon's Tale: Ultimate, there was moreso a layer of bosses. A tier list of difficulty.
First, you had your Overworld ones. Ones you would find normally while exploring. No matter the realm or place there was always one. Usually annoying, but easily surprising to beat once you become stronger.
Then, the next stage was Fixed-Scenario bosses. Not that much different from the Overworld ones, these were ones you fought against during the campaigns or missions of expansions or guilds.
Third, was arguably the most confusing one. Dungeon bosses, they were cheesy, and often didn't play fair. Because then again…the dungeon they were in suited to their every need. Advantages? Fixed. Weaknesses? Barely noticeable even if you decide to exploit it.