Isolated practice on the final boss with save and load states. I was practicing for a worst case scenario with zero health or weapon power, to see if I could beat the boss under those circumstances. It would help for my full run. If you dont take out EVERY gun the ship escapes and you lose the entire level, as far as I know. So you have to also do it quick. The ship does not come back up once its descended. I killed most of the boss on one attempt but never got it. Still the practice should help for the full run when I get back to the boss.