Guardians are the result of the necromorph infection anchoring a torso to flesh growing on the walls. One can usually tell when one is nearby when moaning, groaning, or screaming is heard. However, some have been observed as being silent until engaged in combat.
Guardians are sentries, set up by the necromorphs to defend certain, often mission critical, areas. Unable to move and attack enemies unless they move up close to the guardian, guardians utilize embryonic spawn, similar to a lurker, that they spit out in front of themselves which will aid in attacking detected threats.
Unlike many necromorphs the infected human seems to retain consciousness, hence the constant moans and wails of pain, rather than simply acting as a lifeless host. The circumstances by which this occurs have not been made clear.
An immature guardian is a human torso that has just recently been attached to a wall infested with Necromorph growth and has just begun to mutate. The Immature Guardian still looks very human as it still has an unchanged head, arms and chest until the waist-down, where the abdomen is vertically split apart with the entrails hanging out. The human host is clearly still clinging onto life and will plea to Isaac for help in a weak and disturbingly augmented voice when alerted. Extremely weak and lethargic, the Immature Guardian is incapable of performing its matured brethren's lethal attacks and cannot host spawn. At the very most, they will play dead until approached close-up (or alerted when a light is shone in their face) where the infection will attempt to cause damage by flailing out their hosts relatively-short intestines over which the host has no control and will continue to plea for help. The creatures are 100% avoidable; the only way you can really be damaged by one is to walk up to it on purpose. Don't waste ammo on them, unless you feel like putting them out of their misery. If you use Kinesis on their body, they will moan in pain as you are trying to pull them off the wall. They will die in a matter of seconds if you constantly pull them.
A torso that has been given enough time to mutate and develop in Necromorph growth, the Mature Guardian is the most dangerous of the varieties encountered. The only remaining human feature about them is their badly mutated head, and at this point, they look more like disgusting living, breathing mounds of flesh. They will not hesitate to continuously spew out Guardian Pods when detecting a threat, and will also utilize their whip-like intestines to unerringly behead enemies that get too close to them.
Created and stored within a mature Guardian and spat out by the Guardian upon encountering a threat through a disgusting orifice with great strength to ensure a fair distance travelled from the Guardian, these pods are sacks with a vague shape resembling an embryo. They writhe and twitch, and having been utilized as a defensive tool, they are not made to grow and survive on their own for long. Instead, they are filled with dangerous chemicals and explode when a transgressor steps near them. They are also capable of ranged attack by sprouting out a tentacle and shooting a barb at the source of the threat, much like a lurker. They can be killed by severing their tentacle, which causes them to die and explode shortly after.