What could Zhang Tie do by combining Castle of Black Iron with the crystal ball that controlled the hub of the hieron?
First, if Zhang Tie liked, he could completely turn the hieron's hall into a vacuum state. In this state, he could breathe the air in Castle of Black Iron while fighting the earth demon knight in the vacuum.
In the fight, the earth demon knight would consume its physical strength and battle qi greatly which should be maintained by breath. How many hours could the earth demon knight fight in high intensity while holding its breath, 3 hours or 5 hours?
Second, the laziest method was to keep the gate of the hall closed in super low temperature and vacuum. Under this circumstance, Zhang Tie didn't need to care about the earth knight, he only needed to enter Castle of Black Iron before coming out to pick up the dead fish 2 days later.
