I CAN NOT DEFEAT YUSINDUU

this problem occurs usually if you are a melee class (combat style) and you chose to help rakit earlier instead of adi, that way the fight will become more difficult because there wont be friendly npcs to help and sahaar's heal is not enough,

so there are two things you can do, either teleport away from there like back to the fleet, reset the mission "out of the mire" and then return back and help adi instead of rakit, or if you have a second combat style that is ranged switch to that for this fight only

and lastly, if you choose to help adi and you still die, wait for the npcs to finish off the boss, that can take a while but its doable