mechanics i know of

stay at 25m+
green stuff:siege dmg, easy to avoid by strafing
white stuff:magic dmg, use and to reduce dmg

starts aoe pull and bubble at 50% hp
aoe pull:move -20m to avoid pull then move back to 25m+
bubble:move -15m/use float/use glider, basically be out the water

know any mechanics i haven't listed? comment and i will add it

Tactic

avoid green stuff
right after he use green stuff start rotation:
->->->-> if you need
if you have honor nodachi you can use it before conversion shield but i recommend also using together with or you will take a lot of dmg

use while avoiding green stuff and alternating and when he shoots the white stuff until and are off cd then start rotation again without because it will be on cooldown