The fact of destroying the capital, killing most of the citizens and forces stationed there, and pushing the last standing strong and formidable masters against the cold wall like this was all thanks to this toxic fog.
William got this and also got a way to counter such a despicable scheme. To him, he wasn't going to get affected by this toxin, but the masters following him would.
Alone he wouldn't be able to change anything. And so he needed to find a way to make all these masters walk into the area covered with the fog, without getting affected by it.
He didn't know how the enemy did it, but it seemed the fog wasn't fixed in place as he and others thought. The air in the capital and the area around it wasn't polluted by this fog. Only starting from this zone the fog would appear. And that made him jump to the conclusion that the source of this fog was portable, easy to be carried over to any place.
