I found that the best way to dodge a soul spear is by running to the side of it. The only other way is to roll perfectly, as in a tiny bit before it hits. But that can be hard to do, so if you run to the left or right of it, (in a straight line) I have had an easier time. This may also rely on your running speed. If your a slow runner because of your heavy armor, it probably wont work. Also, if you don't want to deal with that bull crap, then just get close to him and stay BEHIND him. That way, his arrow barrage will be shot on the opposite side which allows you to score more hits. When he gets a fire buff, back off and wait for him to launch homing arrow rain. Go passive then and avoid them until it ceases, and then get close for melee combat. You WILL have to suffer fire damage. An easy way to minimize this affect is to wear armor with a high resistance to fire. (duh) Even with that though, you will eventually have to back off again to heal, and deal with homing arrow rain again. I beat him in 2 tries with this using a +9 Astora Greatsword two-handed. (Of course you don't need this) I also had the grass-crest shield equipped to help with my stamina consumption. Also, if you have it, I'd use the Carthus Arc to buff my weapon.