Thrud's generals had done a nice work building up the mother of all storms but that also meant that arcs of electricity could randomly appear anywhere.
Their light blinded the fighters, their noise deafened if not even burst the eardrums of those too close to their origin point, and anyone who got even grazed by a bolt of lightning would fall to the ground all hot and crispy.
On top of that, in the chaos of the battle even defending against an attack could be fatal for your own allies.
The spells that the Awakened used and especially Silverwing's produced powerful shockwaves when blocked. If another unit was caught by them in the middle of a maneuver, their formation would crumble and the opponent would quickly dispose of them.
