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.
Tried to use a bazooka & cannon in my hands initially, but figured out fairly quickly that I was doing best with the gatling guns.
Edit: Have the game up right now, so I thought I'd give a more detailed rundown of my build:
Body:
Power, FCS & Expansion:
Here's a few screenshots of how it looks (with different weapons than what I used in the boss fight):