Hey,
I want to share my ultimate cheese against Carnifex.
1) craft a napalm grenade
2) get a flashbang
Now, the fight:
a) If you get initiative, drop the incendiary on Carnifex. It's great if he starts burning but it's not 100% necessary. Why? See below.
The AI starts glitching out and performs non-optimally. Carnifex will run all around the napalm taking around half of his HP.
If he starts burning, just burst him to death. You got a few turns, it's easy and enough.
For bonus cheese dosage, drop a flashbang he doesn't resist, then do a knee shot. It's over by then.
b) Carnifex starts, drop the incendiary at your feet
First off, you must survive the initial volley. You'll be netted for a few turns.
Drop the incendiary right at your feet. This depends on Carnifex burning. You must manage surviving the announcer after Carni dies, but the incendiary is still burning. This is actually pretty hard... Anti-heat gear will help obviously but it depends.
You may also drop a flashbang at your feet if Carni doesn't burn. YMMV.
You can also squeeze the incendiary at the right place so it affects him only. I haven't tried that.
If (a) and Carni starts burning, he's done for.
Vae Victis!