"Our forces are mostly light elemental system users. It has been researched to a degree that these brutal monsters can be handled with a few different methods. Flames are somewhat effective but the ashes will still eventually reform them in to undead. Therefore, our flame mages and flying flame swordsman are able to handle the weaker undead easily along with weakening the larger undead here."
The Fel angel in charge had a single hand from an undead brought, he made sure to show around the half ashen appearance as the undead hand was being reformed slowly but surely. Walker had wanted to see this sort of thing so that he could understand how long they would have when defeating the undead. It clearly showed him that the undead would only take minutes to reform when burned to dust. The hand was almost entirely reformed finger by finger as they watched.