Doctors - demented, sadistic beings that take on the personas of medical personnel - only much more preoccupied with hurting rather than healing. They live in towns in any non-freezing biomes, and send out snatchers. They will only siege once you hit 80 population.
They have several castes - all castes feel no fear, and do not need to eat, drink or sleep:
-Orderly - brutish humanoids with large arms and small heads. One of the most common castes. Feel no pain, require no eyes to see. Stronger and tougher on average, but less agile.
-Nurse - female humanoids said to originate from the quiet hills, with large, bloated heads and cracked, metallic masks embedded in them. Require no eyes to see, are more innately agile. As common as the Orderlies.
-Doctor - one of the rarer castes, alongside the other two doctor variants. Have an enlarged arm with three syringes attached to it. Learn wound dressing, diagnosing, surgery, bone setting and suturing at twice the usual rates. Can enrage, increasing their combat rolls. Each of their syringes injects a different medicine - Pain Medicine causes severe pain in the wound as well as pain of any nervous parts; Nausea Medicine causes nausea and blood vomiting; Fever Medicine causes a fever, coughing blood, and reduces disease resistance to 75%.
-Plastic Surgeon - surgeons who see themselves as artists and have modified their bodies. They have three grafted arms - one ends in a pincer, one in a bony club, and one in a jagged barb. It also has an opening in its chest, allowing it to use its lungs and guts as weapons. Learns wound dressing, diagnosing, bone setting, suturing, engraving, leatherworking and butchery at twice the usual rates, and surgery at four times the usual rate. They can lash with their guts, possibly latching on, and can attack with all of their additional limbs - they can also spray directed streams of poison gas, inducing drowsiness, nausea and blood coughs.
-Dentist - particularly sadistic doctors - they have metallic teeth, a drill attached to one of their arms, and a tube protruding from the chest. Learns wound dressing, diagnosing, surgery, suturing, bone carving and intimidation at twice the usual rate, and bone setting at four times the usual rate. Can stab with the drill for a powerful attack, and can release streams of laughing gas, causing dizziness, feelings of joy and amusement, and pain in the lungs or any other part used for breathing.
The doctors use a variety of weapons - a large portion of their set is similar to that of the Cannibals, but they also have large medical saws, syringe-saws, large bone saws (sword skill), oversized scalpels (sword skill), cranial drills (hammer skill), spiked knee-jerk hammers (hammer skill), pipes (mace skill) and syringe guns (crossbow skill, fires syringes). They lack any metal armor, however. They have three unique pets as well that they may bring on sieges:
-Organ Donor - large humanoid with sacks containing full sets of organs on its back. Feels no fear, cannot be nauseated, does not have to breathe. Learns skills at 25% the usual rate.
-Patient - lobotomized humanoids - only a bit larger than normal humans. Feels no fear or pain, learns skills at half the usual rate. Its skull is made of metal.
-Lunatic - humanoids wrapped in straitjackets made of their own flesh. Feel no fear or pain, need no eyes to see, enrage more easily. They do not use weapons, unlike the other two pets. They can either spit globs of caustic bile from a distance, causing bleeding and blisters, or throw up short-ranged streams of the same type of bile for the same effect.
Chud - cannibalistic humanoid under-dwellers. Are a tougher version of underground animal people tribes - they feel no fear or pain, and use metal weapons. Their weapon set is the same as that of the Cannibals.
Infected - the Infected from Left 4 Dead - only in the optional addon. Live in towns in grasslands, savannas, shrublands and forests. They use no weapons and are always hostile, as they cannot even communicate.
Their biting attacks can inflict their contagion, initially inducing erratic behavior, then a flu, then making the afflicted opposed to life and fearless.
They have many castes - all feel no fear or pain and are berserk, and so will attack any non-infected:
-Infected - standard, most common caste. Not different from a normal human.
-Boomer - the big fatties we all love. Has slower top movement speeds than normal Infected, has less agility and toughness. Its vomit causes feelings of disgust and makes one more susceptible to incoming attacks. Male and female Boomers have slightly different appearances.
-Hunter - one of the most common castes - has innate competent combat skills. Innately more agile, can move at higher speeds and climb/crawl faster. Its scratching attacks are more deadly owing to its claws.
-Smoker - long-tongued infected. Has competent innate combat skills and is larger than a normal Infected. Can release undirected clouds of smoke that cause feelings of annoyance and can cause blood coughs. There's also a Multi-Tongued Smoker variant to represent the L4D2 version - it is functionally identical, aside from a slightly larger size and more targetable doodads on its body.
-Charger - big-armed Infected, more rare than most other Infected. Has an innate skilled level in all unarmed combat skills. Can move at higher top speeds - also has a higher innate strength and toughness - shared with the other two Charger variants, along with the skill levels. Its punches can cause very severe damage, potentially knocking their victims away several tiles.
-Ram Charger - based on
one of the Charger concept arts - can only lightly scratch with its tiny arms - primarily attacks by headbutting and tackling - slow attacks, but incredibly devastating if they connect. Smallest of the Charger variants.
-Tripod Charger - based on
another piece of Charger concept art - its head is only a skull, and its scratching attacks are more deadly due to its large claws. Larger than the other two Charger variants.
-Spitter - long-necked Infected - are innately less agile and tough, and also move slower, though not as slow as the Boomer. Spits globs of acid from a long range, causing bleeding and blisters.
-Bloated Spitter - based on
Spitter concept art - can only kick, bite and spit acid, due to lacking arms. Slightly larger than a normal Spitter.
-Jockey - diminutive Infected. Innately more agile and tougher - climb and crawl faster than most other Infected, has the same top speed as the Hunter. Smallest of all Infected castes.
-Screamer - a
cut Infected type - almost identical to normal Infected, save for its ability to scream, which makes its fellow Infected more angry and prone to raging, while giving them a small endurance boost.
-Tank - one of the most rare Infected. Proficient unarmed combat skills, enrages more easily. Moves slowly, and is innately stronger and tougher on average, but less agile. Can hurl chunks of stone from a distance - its only other attacking options are punching with its fists, which can knock one away several tiles, and striking with its lower arms, which is a faster attack but not as deadly.
-Witch - one of the most rare Infected. Proficient unarmed combat skills. Innately more agile, strong and tough, moves at higher top speeds and climbs/crawls faster. Though its the same size as a normal Infected, its clawing attacks are incredibly deadly.
-Meat Wall - based on a
cut Infected - moves the slowest out of all Infected, but is also the largest caste. Has even less innate agility, but is stronger and tougher. Proficient unarmed combat skills. All of its attacks are very slow.
There are also Feral Infected, which appear rarely in forests, grasslands, shrublands and savannas. Similarly to normal Infected, they are fearless, feel no pain and will attack any non-infected beings - however, they only appear as the normal infected variant, and lack specialized castes.