I just read the mission, and well, Fix and the Carver came off as being supremely overpowered, and as a Stu and Sue.
This was their first mission as I understand, and I read their bit in the Halloween cowrite, but nothing more beyond that.
The thing that alarmed me about them possibly being overpowered characters was this portion:
'Fix barely managed to dodge the centaur’s kick. In response, his senses heightened, his reflexes sharpened and most importantly, his nails became lethally sharp claws. Rather than running or dodging, Fix threw himself at Firenze, knocking him off balance. Man and centaur fell to the ground, fighting and struggling until finally, the centaur was dead. Fix managed to shove the body away and climbed to his feet. He fumbled for the miraculously unbroken RA and opened a portal.'
This comes out of essentially nowhere; he becomes suddenly super bad ass and is able to kill a centaur, essentially unarmed, in close combat. A kick from an ordinary horse can cause serious internal injuries that can kill even a full grown man, and those cases aren't even from a horse that thinks its life is in serious trouble. Those are just 'Eek! You are invading my personal privacy!' kicks.
But you have him managing to walk off, mostly in one piece and alive and in good enough health that he's still able to quip and explain what happened before he goes to Medical, where he's still in good enough condition that he walks through on his own power, as far as we can tell.
Reading his page on the wiki fills me with even less confidence that he's not a Stu. His personality section directly contradicts itself in that he's blunt, crude, and direct and cuts to the point in conversations, but he likes having conversations?
He's also described as having adrenal-reactive abilities, regarding the claws, his senses, agility, and balance, but you don't mention anything about strength or superhealing- the first which was implied by his choice of using force to dispatch with the centaur, and the second that you stated outright at the end of the mission. I see no real drawbacks explained on his page- beyond that he can't drink blood for whatever reason because that makes him sleep. This is something that is so incredibly unlikely to happen during a mission- there's no suggestion that he's fighting a bloodlust in the mission, or that he needs to drink on a regular basis- that it's a free power.
I can't comment much on the Carver's sueishness because I have little understanding of the Dresden Files- only read the first book- but this description here doesn't bode well for her:
'The Carver now wore a tight black leather outfit that made her look like the heroine from a spy movie. Her hair was braided down her back, and she had a number of bulges in various places that suggested the secretion of various knives.'
You have her dress in a catsuit- and directly state it makes her look like a spy movie heroine- and threaten to dismember Fix the moment he sees her. If she didn't like the outfit, or felt self conscious in it enough to make her threaten others over how she looks in it, why would she wear it? There's no point to an outfit like that in the PPC unless it's outright required for a disguise within a mission. How would she get she get those various knives out, out of curiosity? Given how tight the outfit is, what is the practicality in concealing weapons under it?
...Beyond that, there's also the disturbing issue of using 'secretion'. Secretion is very rarely used to mean things were hidden away. The more common use and meaning of the word refers to discharge, excretion. I don't think you mean to suggest she's excreting knives out from her skin or other organs.
On that topic, you charged and mocked the writing for a few things that are common and acceptable phrases, like "felt a blush creep up his neck". This is a valid use.
Beyond that, they came off as being viciously unfriendly towards each other, and the mission's tone was more overtly hostile than humorous. These agents seem incapable of an affectionate laugh either at their own foibles or at each other's- vicious comments, mocking, and threats don't count.
Your agents come off as being supremely overpowered, and have a great deal of attributes that cements them as Sues.
I'll be asking other PGs for their own thoughts on all this, because I don't feel comfortable saying anything more than asking you to take a break with writing more PPC works at the moment.