Mytha can be a real pain in the neck if you let her create too much distance between the pair of you. Follow our guide to the tactics involved in this fight, however, and you should have no trouble looting the Baneful Queen Soul from her twitching corpse.
How to kill Mytha, the Baneful Queen
Be very wary of the poison that circles the battlefield throughout this fight. If you torched the windmill earlier on, you shouldn't see poison anywhere else. If you do, and you die during the fight against Mytha, back-track and burn the windmill down to make things much easier.
Stay near to Mytha unless she gets too close to that poison. You can expect her to use a three-hit combo against you with her spear, in addition to a swirling, up-close body spin. The good news is that you can block all of these attacks without losing too much stamina. The bad news is that there isn't a great deal of downtime between her attacking patterns. You'll only be able to get a couple of whacks in between her flurries as a result.
If at any point she creates a little range between you both, get ready for one of a pair of attacks. She might choose to come dashing at you with the pointy end of her spear, a move you can either block outright or dart left or right to avoid. Alternatively, if you see her head begin to glow, get ready to dash to the left or right and dodge the magical missiles she's about to fire. You won't have very long to get out of the way of this second attack, so stay alert.
As long as you try to minimize the distance between you and Mytha at all times, you should be able to severely limit her attacking options. If you avoid the perimeter poison, catch up any distance she creates quickly, and patiently whittle her health down, you shouldn't have too much difficulty finishing off this boss.
As soon as Mytha's dead, make your way through the poison, go through the door ahead of you, and then take the stairs up. Go into the lift, then walk through the door on your right when it stops to gain access to the Iron Keep.
Head back to the first page for the rest of our Dark Souls 2 strategy guide.