An easy way to kill this boss as of 1.04.2 is to use the Serpent Bow in conjunction with Serpent Arrows and Bloodbone Arrows.
Gather the Serpent Bow, 100 Serpent Arrows, and 100 Bloodbone Arrows (Fletched). By this point in the game those items are not difficult to come by. You can back up to the wall when you enter the arena, shoot him until he is poisoned, and then use blood arrows until a hemorrhage, then repeat. You need mighty shot for the distance, and the Arrow's Reach Talisman is a bonus. It took me around 10 Cerulean flasks to have the necessary fp to use Mighty Shot until he was killed.
This boss has around 30,000 HP, and each Poison will do about 2500 damage. In addition to the blood damage, you should have more than enough to kill him. Also note he will drop down mid-fight. If you are far enough away, he will not aggro.
Here is a video that explains the process in more detail. This may be patched in the future: