From bad to worse

When the hellhounds took to the sky the army of death started to feel the real heat as not only were those massive hounds near invisible with their thick and hard skin which was impenetrable, but they dripped of over 2000°C hot lava that instantly burnt a hole in the land that one was standing on much less one's armour. 

The demons riding these hounds were also sinister dropping javellins from the air , piercing their targets one at a time as they picked their killings in leisure. 

No arrows were able to threaten the life of the lava hounds much as the thick skin gave them immunity from any and all attacks under tier 3 strength.

The worst part was that the lava riders picked off men engaged in active combat against a demon legion , creating tactical holes in the defenses of the army of death which lead to more and more troops dying because of the defensive formations breaking.