Additionally, all Animated Weapons, required for the final relic weapon upgrade, will gain their full power; before defeating the NMs, they exist in a weakened state without added spawns. However, the weak versions drop nothing.
Ying and Yang do not need to be killed in order to spawn the Dynamis Lord. However he will be immune to everything until they die.
In order to kill Ying and Yang, they must be defeated almost simultaneously. Otherwise the dead dragon will be resummoned by its twin.
Dynamis Lord will also summon (weaker versions of) the twin dragons when being fought. These versions of Ying and Yang share, to an extent, hate with the Dynamis Lord, however, unlike the initial pair of Ying and Yang, this pair does not need to be killed to win. They will die when the Dynamis Lord is defeated.