This wasn't fog, it was the effect of that materialisation formation, adding more to the monsters, making them stronger.
Be it by elevating their spirit base, or adding more to their size and power, all was possible. In addition to that, there was also a chance for these monsters to get heals and even organ and parts replacements for a limited amount of time.
If that happened, if William let that fog take its time to show its magical effects, then things would instantly shift towards the worst again.
"What? Is it asking us to send all the fire and lava-based masters to stop these monsters?!!! Is he mad?!!!" The king couldn't believe what William just said to his daughter. She instantly contacted her father, using some sort of a special scroll, the same as what Sloth once gave to William.
