Continue your journey with Prima's Dark Souls 2 Guide and Walkthrough!
Reward: Mytha, the Baneful Queen Soul
Watch out for the poison that encircles the battlefield. If there's poison all over, it means you haven't burned the windmill earlier in the area. If you die, make sure you go back and burn the windmill to remove the poison from everywhere except the outer edge of the battlefield.
Stay close to Mytha unless she backs up to the edge of the battlefield where the poison is found. She uses three-hit combo attacks with her spear, as well as a full body spin at close range. Both of these attacks can be blocked with only moderate stamina loss. However, there isn't much delay between her attack cycles, so you won't be able to hit her more than one or two times depending on your weapon of choice.
If she backs away, prepare for one of two attacks. Expect either a dashing spear attack that can be blocked or evaded to the left or right, or a magic attack with her head. If you see the head glow, prepare to move quickly to the left or right, then dodge as the attack approaches. The magic projectiles move quickly, so you won't have much time to react.
If you stick close to Mytha, you avoid many of these attacks. However, she will back away, and you also need to be mindful of the poison surrounding the battlefield. Just be prepared to handle her ranged attacks and stick close to her as much as you can, and this battle isn't all that difficult.
Take down the Queen, then head across the poison, through the doorway and up the stairs. Step inside the lift, then through the doorway to the right when it reaches the top to enter the Iron Keep.