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.
Direct-fire plasma misses, plasma rifle, songbird and grenade launcher. Medium biped build. Plasma is pretty effective since the boss will often stay still, so the lingering plasma damage will eat away at its health/ACS. Probably would have been good to get the tetrapod legs with all the heavy weapons, but I didn't had the chance to purchase them yet.
In general, I had to stay pretty vertical. The melee attack is quite nasty but not too hard to dodge if you're in the air. The beam attack is also relatively easy to dodge with verticality. If you're in the air, you drop to the ground once the beam is 50% charged or so, and vice-versa if you're already on the ground.
Still, took a lot of attempts. Wish I had the pile bunker.
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.