You have broken down the front door, taken out the Lich King's chief physician and beaten down his vampire cadre into a sparkling pulp. Now it is time to take out the Lich King's aerial core by heading into The Frostwing Halls and taking out some Frost Wyrms.
You've seen them everywhere in this expansion and with good reason. The Lich King has been raising an army of these former dragons to do his bidding. They range everywhere from Icecrown, as you would expect, but are also everywhere from the Howling Fjord to Sholozar Basin. These creatures are raised from the bodies of dragons from both the Blue Dragonflight that have been defeated by the scourge as well as any dragon remains found in the Dragonblight.
These twisted forms have no memories of their previous lives nor of the world beyond death. They are intelligent beings capable of strategy, tactics and deception, but their lack of memories of their former life, combined with their unwavering desire to serve their dark master with all the power available to them, makes them very difficult opponents. The goal here is to take out their queen and the last obstacle between you and the leader of the scourge.