What the Fuck are Vampires Anyway?
Vampires are a narrative construct, a memetic lifeform. They live in your head and reproduce through bad urban fantasy potboilers. They're imaginary, but not harmless: they can, and often will, lead to fatal mistakes when dealing with things that can actually bite you.
Vampires are a memetic virus (as per the EE book) and will cause the infected to either believe that they themselves are a vampire, or that anyone who even vaguely fits the infectee's idea of a vampire is a vampire. They will be completely blind to the signs of a Victiscolex infestation.
Blood Slaves of the Conqueror WormVampires don't exist, but Haemohelotes Victiscolex does.
LarvaNo bigger than grains of sand or rice to begin with, little beads of translucent jelly floating freely in the water, waiting for a host. They want humans, they can only mature in humans, but they will burrow into the gum linings of other mammals as transportation. If there are too many any they can find no blood to sustain them they will bloom, turning the waters scab-red and killing everything within in their own death throes.
If they manage to find their way into a human, they will burrow in the tongue and begin to grow, lengthen, solidify. They form pale strings barbed with a single white tooth at one end and splitting halfway down into ten even-thinner tendrils. The first task is to burrow its gangliar tendrils to the brain, as after that is done there's no hope of the victim removing it.
Larvae count as a disease. They can be killed through thorough boiling water, Cure Disease, or the surgery of a doctor. The save vs. poisons does not prevent the infection, but success means that the target is aware of it. The infection takes lvl + INT modifier days to complete.
GhoulThe larval worm has devoured the victim's tongue and finished its work on the brain. The frontal lobe is gone, the lizard brain is rewired. The person is dead, self-awareness snuffed out, but at this point in the process the ghoul has not gone completely feral - they can still use tools, they still wear the rags of their former life, they can mimic the actions of life. Their eyes are sensitive to light, their skin has gone pallid, they feast on flesh and blood.
Ghouls have the vampire powers Darkness Affinity, Unnatural Strength, and Paralyzing Bite
FeasterThe ghoul has reached the precipice of metamorphosis, and the transition to its mature form requires flesh. They are filled with a terrible hunger, distending and bloating on accumulated mass as maggots on a corpse. When the time has come, they will drag themselves to a body of water - fresh, salty, sewage - for the final change.
Feasters have the powers Darkness Affinity, Claws, and Poisonous Bite
CystAfter the cocoon of pockmarked skin bursts open like a rotting tomato, the thing that remains is not entirely a car-sized mass of tumors, not entirely squidlike, and not entirely unlike a jellyfish made of raw ground beef. The cyst is now capable of spawning viable larvae, and has developed a method of achieving this while simultaneously increasing its own mass - specialized larvae that cannot progress past the ghoul stage will be spawned, and these lureghouls will then be used to draw in unsuspecting and chemically-addled humans to the cyst, where they will be broken down for meat, bone, and zygotes.
Lureghouls have the powers Darkness Affinity and Hypnotic Gaze.