Kind of an Airhead (Part 1)
First, the Void Spell condensed the humidity in the cave into a layer of frost that covered living, undead, and constructs alike. It also weakened Lith further, but he didn't care, knowing what was about to happen.
The temperature dropped by dozens of degrees, sapping the heat of humans and beasts. At the same time, the cold sealed the joints of the armor of the undead and hindered their movements.
At that point, the water comprising the ice instantly broke down into oxygen and hydrogen.
The cold wave of Frost Fire turned into heat that set off the flammable gases into a ground-shaking explosion. The blast caught the Dread Knights by surprise and with the floor slippery from the ice, they were sent tumbling like everyone else.