Really deserves to be called legendary. Her shout shaves away your health, stamina and magicka and her breaths are nothing to sneeze at either. If you don't have a plan when you challenge her, you're definitely going to die.
Strongest of the unnamed dragons. Like the Ebony Warrior and Karstaag, she's effectively on the level of a final boss in Skyrim. For that matter though, her design seems rather simple. Her spines are small and few, and she's only got one pair of horns. However, her eyes in particular are special. She has four small white eyeballs placed into her eye sockets.