This boss fight has two main parts: giant armored-beetle Boaz and flying humanoid Boaz. I found it helpful to use the Boran X for the first phase, since Kurtis can jump and backflip—albeit in a limited way—while using the gun.
If you've just done the "Dodgeboaz" achievement/trophy, you can either reload your level-start save (so all of your ammo is available again); go after the 2 ammo pickups (1-2), detailed in the main walkthrough; or just keep going.
Begin with the same tactics we used for the achievement: Equip the Boran X. Run toward Boaz (so Kurtis takes aim) and shoot at her human face.
Backflip away when she lunges, then continue firing.
You'll notice her health bar depletes and green liquid sprays from her wounds when your shots are connecting. Don't waste bullets firing at the armored bug parts.
Once you've done enough damage (about 10 direct hits to the face), she'll begin launching blobs of green goo from the venom sacs on her sides. Stop shooting, so you don't waste ammo, and side flip out of the way.
Side flip once or twice more.
This time, instead of moving around behind her, run/jump in close to her side. The goo should (mostly) sail over Kurtis's head, and he should target the active venom sac. If he doesn't automatically do so, you can press Roll to change targets. (Note that you can only damage the sacs when they are open and gushing.) Shoot the sac a few times it until it is destroyed.
You'll know you've done it when the slime stops and the dark-colored, chitinous flap over the sac disappears.
After you've destroyed the first venom sac, Boaz will take a moment to collect herself, then turn and lumber toward Kurtis once again. If things have gone well, and Kurtis hasn't been poisoned or lost too much health, you may want to quick-save, but don't overwrite your level-start save, in case you run out of ammo and need to try again.
If Kurtis does get hit by a blob of venom or stands in one of the green puddles, he will be poisoned. Either reload and try again, or use an antidote or large health pack. (If possible, try to fight on for a little while while poisoned, to conserve antidotes.)
Between volleys of goo, Boaz will sometimes spew green liquid from her fanged mouthpart. This is different from the stuff that comes out of the sacs. It doesn't inflict poison damage, but the stream can knock Kurtis off his feet, and by the time he gets up again, she's closing in for the next attack. Try to flip to the side a few times...
...to avoid it.
Then wait for Boaz to turn toward you and repeat the sequence:
Shoot her in the face, backflip out of the way as she lunges, then shoot her some more to bring on the "shelling."
When the goo starts flying, side flip a few times to avoid it.
Then run/jump in close...
...and shoot one of the venom sacs.
Repeat for the two sacs on her other side. Depending on how long it takes you to completely deplete her health bar, you may not need to destroy the fourth venom sac.
But destroying all four will definitely bring her down.
When she runs out of health, she keels over. Defeating the giant mutant bug (1) counts as one kill. But of course, it's not that simple.
Cutscene: Kurtis turns away from the huge bug. "That wasn't so hard," he quips. But before he can catch his breath, the humanoid Boaz wriggles free from the insect corpse. She stretches her diaphanous wings, lets out a shriek, and takes to the air.
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