Why Flame Hatchlings?
Because Onyxia's lair was filled with flames.
Some were caused by the unique environment here, which was why Onyxia had chosen this place to build her nest.
But most of the flames came from the Dragon's Breath Onyxia had unleashed to create a more comfortable environment for herself.
In an environment filled with flames and heat that could not dissipate, her dragon eggs would absorb the fire elements and hatch into Flame Hatchlings. She would enjoy it all the more, too.
But what was pleasant for her was a disaster for other creatures: flames erupting everywhere and intense, searing heat.
Few could withstand such terrifying flames as the Black Dragonflight could.
Now, to stop the humans who had come to slay her, she unleashed even more Dragon's Breath, making her surroundings hotter still. Fire Elementals surged throughout the entire lair.
However...
It didn't do a damn thing.
"Mage Corps, Summon Water Elemental! Use Frost Magic without restraint! Frost Nova! Cone of Cold! Frostbolt! From now on, no one is allowed to use any Fire Magic against the enemy. Frost Magic only!" Jaina's orders were precisely targeted.
Soon, over a hundred water elementals moved to the front, absorbing the waves of heat inside the cavern. The mages took turns in an orderly fashion, casting Frost Nova, Cone of Cold, and other spells ahead of the main force to freeze the ground and air. As the ice melted and sublimated, it carried away vast amounts of heat.
The cavern's temperature returned to normal, even becoming slightly chilly.
"Attack!" Varian Wrynn commanded.
The main force advanced slowly and steadily. None of the Dragonmen could harm them. So far, the force of nearly a thousand had not suffered a single casualty, and only the archers, warriors, and mages had even fought.