Baneful Queen Mytha
The Baneful Queen Mytha is found atop the Earthen Peak. She is uses melee and magic, and is fought in an arena full of poison.
Weaknesses
The Queen is extremely weak to Fire. She will take much higher damage from any weapon covered in flames.
Pre Battle
To make this fight much easier on yourself, go to the Central Earthen Peak bonfire. Turn around and head straight from the bonfire towards the windmill. On the right side is a small ledge that you can walk out on. Do so with a torch lit and a prompt will appear allowing you to burn the windmill. Do this, and it will actually drain the poison pools throughout the area, including the one in the boss fight. If you're human it also becomes possible to see a summon icon near the boss enterance for Jester Thomas.
Melee Characters
Melee characters will need to be cautious during this fight, as the Queen has a few attacks that can be devastating to you. The most notable one is when you are up in her face, she will lean back and then suddenly lean forward trying to grab you. If this lands, you will take tons of damage, so make sure you never stop moving, constantly strafe around her sides. She will also try to hit you with some basic, sweeping melee attacks, these should be easy to block, or roll away from. The tip of Mytha's tail can be severed, which takes away her sweeping attack.
She will occasionally cast magic, which can be devastating. When she goes to do this, she will usually move away from you, so just keep the pressure on her by staying near her, and this will encourage her to melee you more often. If she does go to cast a spell, be prepared for a last second dodge, as your shield won't likely block much damage. She is very, very weak to fire and can also be stun-locked, so bring a fire enchanted weapon and you will kill her in a matter of seconds.
Ranged Characters
Casters and archers won't have to deal with much melee from the boss, but instead will have more magic coming their way. It is best then, to use a shield that has a higher magic block rate. Of course dodging is the best option, but sometimes it isn't always an option. When it comes to hitting her, just pick your shots in between hers, and try to use Pyromancy, as it does a devastating amount of damage to her.