Enemies are divided into two groups, Mutants and Creepy Mutants.
Mutants
Regular Mutant
Most patrols of mutants consist of 2-4 regular mutants and 1 Mutant Leader. They are the most human looking and common variety of all the mutants. They are the main “group” of mutants, from which the skinny mutants seem to have split off. The males may be decorated with human skulls, masks, bones, feathers, etc., sometimes wearing necklaces made out of CDs or makeshift lamps over their heads attached to poles on their backs.
Skinny Mutant
Skinny mutants are the second main faction of mutants, the other being the Regular Mutants. They are more aggressive and more hostile than Regular Mutants, and will immediately attack the player unprovoked as they are hostile from the beginning of the game. Skinny Mutants are distinguishable from Regular Mutants as they are much skinnier, smaller, are covered in blood and dirt, do not wear clothes of any sort, and will move on both arms and legs. They are faster than Regular Mutants, but are weaker in both health and attack damage. The patch notes for v0.54 indicate they can only carry sticks, rather than actual weapons.
Pale Mutant
Pale mutants will often be found traveling together with skinny pale mutants or found in caves together. Pale mutants stand tall, and move in a very human like manner. They, along side skinny pale mutants, are the only kind of mutants found in the caves. Pale mutants have the same complexion as skinny pale mutants and are slightly larger than them.
Pale Skinny Mutant
Skinny pale mutants will often be found traveling together with pale mutants or found in caves together. Skinny pale mutants stand hunched over, and move in a more primitive, skittering fashion. They, along side pale mutants, are the only kind of mutants found in the caves. Skinny pale mutants have the same complexion as pale mutants.
Painted Mutant
Painted mutants are their own distinct group. Painted mutants come in male and female forms. Regardless of gender, they will have small black crosses all over their body. They are noticeably stronger and faster than their counterparts, the regular mutants. Painted mutants have been observed traveling with fire mutants. Like the regular mutants, painted mutants usually follow a leader. They can also be backed up via intimidation, like regular mutants.
Masked Mutant
The Masked Mutants are a late-game tribe of mutants, added in patch v0.55. They resemble pale from the neck down, but they have the faces of plane passengers and other victims stitched into a mask that they wear on their head. Some of the pale mutants in the lab have been replaced with masked mutants. They are similar to masked skinny mutants though are much smaller, they always travel together though have very different stats and behaviors.
Masked Skinny Mutant
Masked skinny mutants are similar to masked mutants, though are much smaller, they almost always travel together though have very different stats and behaviors. Masked skinny mutants are almost exactly the same as skinny mutants and pale skinny mutants, they are however the strongest of all the skinny mutant types. They are faster than masked mutants, though they are physically weaker.
Fire Mutant
They are usually sent to attack the player’s base. They can however occasionally be part of day and night Patrols, if the player has highly raised hostility. The fire mutant carries a fire torch with several tennis balls hanged on his belt. They will attempt to throw the lit tennis ball at the player if he is a certain distance away from him, inducing burning damage. If the player is in immediate striking distance, the Fire thrower will attack with its torch instead.
Dynamite Mutant
Dynamite mutants were easy to spot; they are very orange in color and carry a stick of dynamite and a flaming stick. They have on decorative shoulder pieces, a loincloth, eyeliner, and sometimes warpaint. Dynamite mutants are bald and barefoot (like any other mutant). This enemy was removed in update v0.28d
Creepy Mutants
Armsy
They are taller than the player and normal mutants, along with being significantly stronger than them. They will bellow angrily intermittently, so the player can usually hear an Armsy before it is seen. As with all creepy mutants, it is best to kill it from a distance with fire and explosives, so that it does not get a chance to hit.
Virginia
Like the Armsy, it appears to be formed by two (possibly three) bodies that are struggling and writhing against each other. The Virginia has 6 legs, claw-like feet, breasts, and 6 malformed arms (four of which appears to have been split in half). The Virginia is also the only creepy mutant with visible genitalia, as the ♥♥♥♥♥ of the front female body appears to be extended along the underside to connect to the ♥♥♥♥♥ of the rear female body. The Virginia has no facial features. However, the front side of the Virginia appears to be the side with the two least malformed arms with functional hands.
Cowman
Unlike other Creepy Mutants such as Virginias or Armsies, Cowmen have facial features and don’t appear to be formed by multiple bodies though they are also taller, wider, and stronger than Mutants. Cowmen can be said to resemble a grotesquely obese human or an early human fetus as evidenced by the distorted, smoothed out facial features with tiny arms, a protruding stomach, the lack of genitalia, and the space between the legs.
Mutant Baby
Mutant babies can be found in caves, though will appear above ground on or after day 7 in the company of a Virginia. They can sometimes go wandering away from the Virginia seeking the player though will generally stay with her. Mutant babies have one leg, with a stump where the other should be, as well as only one normal arm, having a smaller and clawed one as the other. They screech like angry birds, and they will crawl towards distractions, such as the player moving or a lit flare. They can be often heard before seen, due to the squelching wet sounds they make as they drag themselves across the ground. They sometimes give an almost human-like cry when killed, creating a very unsettling feeling in the player.
Blue Armsy
Very rarely, a blue skinned Armsy may be encountered. They have more health, and it may be faster or do more damage, though this would require confirmation. The player is advised to take extra caution against a Blue Armsy. They can be found on the surface traveling with pale mutants and even another blue Armsy beginning around Day 18. Although called “Blue Armsy” they appear more gray like the pale mutants in direct sunlight.
Blue Virginia
Very rarely, a blue skinned Virginia may be encountered. They have more health and are both stronger and faster. The player is advised to take extra caution with blue Virginias. A blue Virginia can be found in the large wet cave room near the modern bow location. Around Day 20, they will begin spawning on the surface and may often travel with a regular Virginia, a Cowman, and two Armsys, one of which could be blue.
Worm
The Worm Creature appears to be made up of multiple (over a dozen) smaller entities that look like slugs with teeth on one end. These smaller creatures do not possess much power on their own, but they seem to have an incredible hive mind attacking behavior. There seems to be a number of ways the worms can spawn: a large number all at once, only a few, and a single one. If all the worms spawn at once, they do so with great force.
End Boss
The End Boss is an enemy with several appendages, created from a small child named Megan Cross, using the Resurrection Obelisk. It can be found in the research lab and as a late-game enemy. It is the final boss of the game.