Ah, Gyorg, good ole' gargantuan masked fish..hmm
First step: Calm down! He's easier than you think!
Second step:Frantically search for bubbles before
they arent there!(meaning he's either ramming the platform or soaring towards you)
Third step:If and when you see bubbles, shoot an arrow at him
and wait for him to lazily float around
Fourth step:equip the zora mask and dive underwater
and use the electric shield..the buttons are just hold R while swimming
Fith step:Repeat all above steps until there's no tomorrow for him
Sixth step: Pat yourself on the back! Congratz', you've defeated the devious Gargantuan Masked Fish, Gyorg!
Good luck!