Killing the Sea Spider!
The best way to squash this spider in the first phase is to use high impact weapons. The spider has a much longer stagger period than most other bosses you encounter, being long enough that melee weapons have enough time to recharge and hit again before it gets up.
The best I found for this was the Ashmead and the Plasma rifle, using the ashmead for impact to knock it down and the rifle’s charge attack to sheer damage while it is weak. Use assault boost to stick close to it to prevent it’s heavy laser from hitting you, as it can’t aim that low. IF it rears back for the smash attack, move under and past it or back away before boosting at while it recovers from the attack.
Once it hits about 50% health, get some distance so it doesn’t hit when it takes to the air before immediately boosting at it to avoid the explosive laser attack. If you can get above it, take advantage as it has almost no attacks to target things above it after the phase shift.
In this phase it actually has an even longer stagger period leaving very open to attacks, but once it recovers, it almost always uses the spinning laser attack. Get far away as this attack can stun lock you and absolutely destroy all of your health.
After it finishes go back to boosting and punishing it with the ashmead and the charged plasma rifle. And viola, should die pretty easy to this tactic. If not…. I guess this play-style isn’t for everyone.