I love the game, and the fight is so much fun, I only have a few things i'd like to see differently.
first off, I feel the sword is a bit too forgiving, for example when you are doing the ocarina of time reflect, timing is almost absent, I was able to complete both sections of reflecting by just spamming m1, maybe just reduce the hitbox on the front of Billie, or make the projectiles move faster? I also noticed hitting the minions is also too easy, like you hit them behind you, though I do understand that since the boss fight is meant to focus on the platforming, and forcing you to aim your swings as well may become a but overwhelming.
and the second and last thing I noticed, is that the shark plays almost no part in the fight, which I don't love, it never came into play for me, but a cool mechanic I think would be if throughout the fight, if the shark dove out and broke more of the map forcing the player to have to avoid more shark holes, it could also be cool if the shark jumped out of the water to attempt to crush the player, I think that could be fun.
Other than these the game if just amazing, keep up the great work and you have my purchase when the game comes out. Best wishes.