Giving the TF2 mercs TMA fears because I can
Scout - Hunt
I'm starting off where I failed but uhhh oh well. Scout was The Hunt because I couldn't think of anything else, but I feel it works due to his speed, y'know the whole idea of the chase. No one is going to hunt you down like a Scout player will.
Soldier - Vast
This is an odd choice, especially considering the anger Soldier is very often characterised by. The Vast was chosen because rocket jumping, THE soldier mechanic. It's perfect for quick travel over large spaces and the fear of being shovel-smacked from above out of nowhere is some kind of Vast manifestation.
Pyro - Desolation
An obvious one, Pyro loves fire, fire is the Desolation's whole thing. It also creates an interesting contrast, especially considering the way Pyro views the world, while the destruction they leave in their wake is considered horrifying by everyone around them.
Engineer - Web
Another strange one, but I think it fits. Engineer is part of the Web less based on his character and more where he fits into the TF2 lore. Serving the Administrator and the whole Conagher legacy pretty much tying him to the Gravel Wars, many connections and the ability to tug at a string to make something happen.
Heavy - Slaughter
This is unsurprising. Heavy wields a 120kg mini-gun that's made specifically to kill you quickly and carry lots of ammo so he can do it 3 times over. The man that fights with his fists and recounts torturing an Engineer as a 'funny story' is nearly a perfect choice for the Slaughter.
The main issue with this is that Heavy is not a very angry person. We usually see a considerable amount of anger in Slaughter avatars, but from comic appearances, Heavy is remarkably calm.
Demoman - Eye
Not only is it deeply ironic, it fits. The Eye can manifest in knowledge and curiosity which would coincide with little Demo's curiosity, opening a book he's told not to and losing his eye. Also there is something to say about Demoman being strangely tied and pulled towards the supernatural and magical. Sounds a bit like this archivist I know, actually.
Main issue with this idea is that Demoman isn't all too aware most days, his whole gimmick is being drunk all of the time. (Though that could also link back to the addiction parallels we see in Jon.)
Sniper - Dark
He's a Sniper, why would he want you to see him? The Dark is perfect considering his career and what makes it easier to do his job. He also plays right into the fears of The Dark, something lurking and hiding in the shadows which could be a threat.
Medic - Corruption
Not only is it some more irony, but it's irony that fits perfectly. Is Medic a good doctor? He's not even a doctor. Will he keep you from dying? Probably. Are you going to end up the result of some horrific experiment? Yes!
While it fits almost perfectly, the TF2 Medic doesn't do much with disease, usually it's an ill-advised surgery, not the parasites or sickness the Corruption is known for.
Spy - Stranger
Do I need to justify this? It's his whole schtick, pretending to be others to gain trust and backstab you. He does the stealing skin stuff with paper masks instead of skin and it's funny