well, i also tried using smolder dragon and eternal schism of dual sword and got it to the point of rage, but eventually got killed..
i killed the white fatalis with akantor set and akantor bow, with bombardier jewel activating the bomber skill, i brought with me book of combo 1-4, 10 large barrel, 10 gunpowder, 3 large barrel bomb, 2 large barrel bomb +, and 10 scatterfish
i try to bow him up when his on land..
if he flies up, that is the time i deployed 2 large barrel bomb + in his shadow beneath it.. then wait for him to go down in a distance and targets the bombs making it explode, this i noticed caused a great deal of damage to him, i combined large barrel with gunpowder to create large barrel bomb, then combined it with scatterfish to create large barrel bombs +..
also if his on top of the tower and his rage is unbearable, try using farcaster, and you will go directly to the starting point with lots of supplies ready for you to take up..
hope my way of killing fatalis helps you..