It was quite obvious that Nial and his Devils wouldn't be enough to deal with all Dungeon breakouts at the same time. There were simply too many dungeons in the mountain-range region to control and conquer. It would be hard to cover the distance and fly around all obstacles while conquering the dungeons, to begin with.
However, Nial was not discouraged by this. On the contrary, he was ready to test out a few things that piqued his curiosity. One thing in particular that attracted his curiosity was how strong the Curse Hodur's Heir had become.
It was considered a linked ability since the strength of the Curse increased proportionally with the cultivation progress of Nial. Nial hadn't used the black miasma of his Curse for quite a while. Hence he thought that it was about time to figure out how powerful it had become.