Sure, only because I like you so much Profesorek.
Here at 0:55 take a close look at when the DL shoots it's fire bomb. Pay attention to which sqms it lands on and you'll see and understand it. Then you can fast foward and you'll see that the fire fields are in exakt same condition they were later in the cam.
Through out this whole cam you can see it happen constantly as they are fighting. They are using destroy fields before placing magic wall. As example look at 16:40 you can see Xanadu uses a destroy field then uses Magic Wall.
Anything else you would like me to clarify?