I have figured out how to kill it so fast that its stunned twice before any ad waves happen but then they still happen so the second phase doesn't start despite how much damage I have done
What's interesting about the Bilewater boss is that his attacks that spawn adds, don't REALLY spawn adds, like the adds just leave after attacking once. So, you can consider his "adds" to just be disjointed attacks. Actually one of the few good design decisions from that boss.
now I fight a boss that does double contact damage, melees you if you ever approach, spams full screen projectiles with random movement that disable healing
can't do anything fun like grapple spam so this fight is just boring wait halfway across the screen and hope you aren't 1 pixel too close to the projectile arc