fern

The Web:

This one is obvious and can be no one other than Lord Vetinari himself. An absolute master of subtle manipulation and long term planning, Vetinari is the perfect Avatar of the Web. He creates a reputation of pervasive fear and makes people believe that he could do away with them at a whim, despite him never once killing a single person who wasn't an irredeemable criminal of some sort, and even then usually giving them chances to redeem themselves first. This being the case, I'd say Lady Margolotta is also an Avatar, and the one who exposed Havelock to the Web in the first place.

The Hunt:

The most stereotypical aspect of the Hunt is manifested most by Wolfgang von Uberwald, the textbook Hunter who chases and kills for the thrill of it. Both Sam Vimes and Angua hear the call of the Blood, but both refuse to heed it, and so aren't Avatars. I'd argue that there's another Avatar of the Hunt fulfilling the other role, created by the Hunt to be the perpetually hunted, the never caught but ever pursued white stag/ golden doe, the one, though not only, Rincewind.

The Eye:

One Avatar is Jeannie and every Kelda before and after her. The Kelda sees everything and knows what has happened and what will. The alternate answer is Blind Io, given his literal eyeballs that float around and also that he's cognizant of everything that goes on in the Disc, and that everyone knows he's watching.

The Spiral:

The Elf Queen. The undisputed master of illusion and deception, creating false worlds that operate on her rules, trapping people in unreal dreams they cannot escape, making them see and believe what she wants them to see and believe. Bel Shamharoth is also a possible answer given how he distorts the senses and feeds on those he traps.

The Buried:

Albrecht Albrechtsson. Knockermen are undoubtedly Avatars of the Buried, with the complex stew of fear and reverence they feel for the underground, and Albrecht is the lowest among them. Agi Hammerthief is probably the only fully realised Avatar of the Buried, who dwells beneath the Disc where no one will ever reach him.

The Flesh:

The Igors and Nutt. The Igors for obvious reasons, their affinity for tinkering with bodies, and their indisputable understanding of the fact that meat is meat, and as such can be used for a lot more than its original intention. Nutt because he is a creation of said tinkering, flesh made warped, with a living engine of meat inside him.

The End:

Mort and Bill Door, and possibly every zombie. This really needs no explanation. Mort stepping into his Master's role is the textbook descent of a human into Avatarhood, developing strange powers and slowly becoming Other. I'm not counting Death because he is the personification of the thing and isn't human enough to qualify as an Avatar. Susan is possibly some kind of Agnes Montague analogue, born from the force itself.

The Slaughter:

Carcer, the Gonne, and Cohen the Barbarian. Carcer killed for the fun of it with no care for reasoning, consequence or morality. He WAS a one man slaughter by himself. Cohen's existence was also very similar to Carcer's, albeit he killed far more people and lived by a Code that ensured that though he mass murdered on the regular, he always did it with the same honesty as a man hunting for his next meal. As such perhaps Cohen was more an impersonal personification of the Slaughter like the Piper rather than an Avatar of it. The Gonne was more an a artifact that channeled the Slaughter into whoever held it, be it D'Eath, Cruces or even Vimes.

The Corruption:

Vorbis and the Cunning Man. Vorbis absolutely embodies the toxicity and insidious creeping infestation of the Corruption. He pollutes organisations and people, changing them and turning them into versions of himself, utilising extremely unhealthy relationship dynamics in order to do so, creating an atmosphere ripe with fear, desperation and despair. The Cunning Man is similar except his method of corruption is more direct than Vorbis's ie literally taking over the body of his victim while subtly influencing the minds of those around him when he's less corporeal. His presence is filth of the mind and stench of the soul, and incites disgust and fear among those aware of his true nature.

The Stranger:

I had some trouble with this but finally decided on Susan and Lu Tze. Although one would intuitively put Susan under The End, in practice the characteristics she actually exhibits line up more with the Stranger. She walks unseen among others, unknown in the places she passes through, never usually staying very long in one place unless that happens to be her dwelling at that time. Her presence unsettles people. She doesn't fit in among others and has always been set apart. She's too undead to be truly alive and too alive to be truly undead. The only people who really know her are Death and Time. To everyone else, she's a stranger they see sometimes.

And Lu Tze, of course, is just the Sweeper. No one knows the first thing about him apart from the fact that he happens to be there. He's a part of the background of whenever he is. If anyone ever truly Looked at him, and actually noticed what they saw, that he's in fact a stranger in their midst, the first words out of their mouths would be "I do not know you"

The Desolation:

Stratford, Spider the Rat King, and Ipslore the Red. Stratford was a motherfucker who would bleed every last drop before abandoning the corpse he created. This was a bastard who, wishing to cause Vimes as much pain as he could, chose to target his son rather than seek him out directly. A man after the Desolation's own heart. Spider was out for everything the humans had. It wanted their utter ruin and destruction and was well on its way to achieving it. And Ipslore attempted to destroy the whole world with his resentment, using and abusing his own son as his instrument to do so, and would have succeeded too, if it weren't for some idiot with a half brick in a sock.

The Extinction:

The Things from the Dungeon Dimensions. The Extinction is the end of the rule of Man and their replacement with the horrifying Other. And there's nothing that fits that description better than the Things from the Dungeon Dimensions, constantly seeking to bring about exactly what the Fear is.

The Lonely:

This was difficult to decide as well, but I believe the First Tooth Fairy might qualify. Living literally locked up in a bubble separate from the rest of reality, it lives apart from everyone and everything else, keeping alone for all eternity. Additionally, I believe that every living witch(with the exception of Nanny Ogg) carries a piece of the Lonely inside them. Its influence never goes away, and those who succumb to it are the ones who become cacklers.

The Vast:

Tiffany Aching and, funnily enough, a Simon once again. Tiffany's primary source of power is that she is, at her core, something far bigger than herself. She may be just Tiffany but she is also Land under Wave, the power and will of millions of years of life before her. At her most powerful she is aware of EVERYTHING, from the bones of the flint beneath the chalk to time itself to the stars being born in the distant sky. She is small but she is also Vast. And Simon sees the whole universe and truly understands what he's looking at. He sees and understands more than he can express and his knowledge of the Vast almost approaches comprehension.

The Dark: