Brilliant, simply Brilliant. Though, I have to wonder what would happen once the Cannabis People and the Scooby Doo Gang encountered one another...
This isn't really so much a Faction, as it is a force of nature.
#15: The Lacus Scourge
After the Cataclysm struck, dozens of genetically engineered bio-weapons were unleashed onto the Wasteland, and most of these diseases are still around. The worst of them, in terms of sheer destructive potential and psychological trauma is by far, the Lacus Scourge, or, the "Hollowing," named after the Facility it escaped from, and it's twisted effects.
The Lacus Scourge is an extremely virulent Fungal infection that affects the central nervous system, rendering the victim immune to most pain and triggering an almost constant high. It's victims are driven to unimaginable rage, and a feeling of mad starvation as they are fed upon by the Infection, driving them to viciously attack all who don't display symptoms of the Contagion. The spores are collected under fingernails, inside the mouth's saliva, and the blood itself. Those who are infected begin to grow nauseating, yellow-green, thick, ridge-like protrusions on the skin all over the body, these ridges are Fungal Colonies. The skin that isn't covered by ridges begins to lose all pigment, as do the victim's eyes. After a week, the Fungus begins to slowly rot the victim, and dramatically slows the victim's metabolism, allowing them to survive without food for weeks. As the Fungus progresses, it's victims which were once intelligent and capable of rational thought, become mindless, enraged cannibals who feel nothing but total hunger, what's worse, it's victims know that they're losing what makes them Human, but at this point, they don't care about anything but feeding, hence the name, The Hollowing.
The Hollowed are entirely capable of effectively wielding crude melee weapons, and some retain their past aptitude for firearm usage. They gather in massive cannibalistic roving hordes, numbering in the hundreds, and during severe epidemics, thousands of bloodthirsty monsters, that were once completely ordinary Sapient creatures. They are very different from cliched Zombies, they can feel pain, and emotions, but both are completely overwhelmed by sheer rage and hunger in all but the strongest-willed individuals. Often, less advanced Hollowed can use basic tactics, such as flanking, and taking cover, but most prefer to charge screaming at the top of their lungs. One of the Hollowed fights as if he were perpetually drunken, feral, starving, enraged, and high on speed, heroin, crystal meth, and bath salts. Adding to the horror of fighting them, simply being in a close enough proximity to the Skin ridges will spread the Plague, let alone bites, scratches, and the faintest of blood-on-blood contact. Even without these, there's still the concern that someone will accidentally ingest a Spore, and go feral days after the fighting has ended.
At first, the Infected are completely intelligent and rational, but feel as if they were starving. After roughly half a week, the Infected will begin to engorge themselves on all food available, but gain no weight, instead becoming thinner and thinner, and more and more desperate. When a week passes, they begin to crave meat, any kind of meat, but specifically sentient meat, which is the only food group with enough protein to keep them from dying of hunger. Most begin scheming to capture and eat people, but only a few of these actually do it at this point. When two weeks pass, prominent ridges begin to form, and the Skin starts to grow pale, victims become so hungry they actually start to eat people, any people, family, friends, it doesn't matter as there's meat to be had. At this stage, the Fungus has already set up in the brain stem, and curing the disease is impossible. When a month passes, they start to congregate in large groups of Infected, and begin openly killing and eating people, perhaps half manage to escape, they continue to spread it later. The Contagion spreads throughout the entire body, once one of the Hollowed begins to lose muscle coordination and loses the ability to speak in favor of moaning, the end is near. Most of the Hollowed last only three months, before the Fungus completely consumes them and must find a new host.
When a horde of the Hollowed gather, their respective Fungal Infections begin to grow much faster, shortening the time until an Infected Person is a blindly psychopathic, chronically starving, rage-addict from two weeks to only half a week. Occasionally, one of the Hollowed will break off from it's Horde to wander on it's own, making it difficult to completely stamp-out an infestation. The Hollowed are bone thin, but they are filled with unnatural strength and endurance. Due to the Fungal Infection, their blood becomes slightly green-tinged, and it is very unwise to injure them up close, as a spraying artery spells almost certain doom. Only the most grievous wounds will faze them, but even then, eight out of ten times they'll shrug it off, get back up, and go back to beserking.
The Lacus Scourge, fortunately, simply kills almost all animals and plants it infects, people are the disease's primary target. Perhaps due to design, the Lacus Scourge is not airborne, or waterborne, although spores can hibernate, to survive in the most inhospitable environments possible for decades, until they detect that they are inside of a potential host. Because of this, the best way to deal with a Pandemic is to simply kill everything within twenty miles of the epicenter, torch the remains, and spend a month or two hunting for stragglers. Even though the Lacus Scourge is inevitably lethal to it's victims, a massive regular dosage of high-powered anti-fungal drugs will stop it in it's tracks early on, the problem is detecting the symptoms in time to make a difference. The last major Hollowed Pandemic was a few decades ago, but very rarely, sporadic outbreaks will pop in remote areas and cause twenty or so Infections. Efforts towards completely eradicating the Lacus Scourge are possibly centuries away, as long as a single speck remains, the Scourge could begin anew.