Greyflames

Greyflames are perhaps the most universally destructive Blight. They destroy indiscriminately, not caring if they strike at living or non-living material, and feed upon the energy of that destruction. However, because they require so much energy to continue their swath of destruction, they do not gain vitality from this, merely sustenance. 
Greyflames appear as amorphous patches of fire, save that they have no color. They may briefly assume a humanoid or animalist form when attacking, but never keep one shape for long. Their motion is also reminiscent of flames: jerky and rapid.