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The dragon one is generally a culmination of the Oasis's introduction of the tanking mechanic.
Basically, some Tank buster attacks need to be taken by a tank class. Tank classes will have a skill that'll increase their enmity and make them much more likely to be hit. The dragon won't only  have that mechanic, but that's the main new one. There's an option in the tactics menu mid-battle that elaborates some on the  boss mechanics you may see