The boss is (I think)
Coral-fueled SEA SPIDER
What loadout did you use?
I used
Plasma blade and pilebunker left hand. Laser rifle and vertical missile launcher right side. Reverse joint feets.
I feel I did not "get" this boss. The only reason I was able to win was because pilebunker charged damage output was insane. Everything else felt like it was tickling the guy.
How was second phase with this build?
It went pretty quick. The plasma is a bit less effective, but the boss isn't all that maneuverable in the air.