Azoth, originally known as slendersludge, is a black, organic tar-like substance that Slender Man sometimes leaves behind. Its connection to him is uncertain, though it's been theorized to be Slender Man's equivalent to blood. Large pools of it have also been found scattered throughout The Path of Black Leaves. Its first appearances were in early Slenderblogs such as Let Us Keep Living, Exilis Veritas and The London Librarian. In those blogs it was shown being thrown up by a Proxy under mind control when they were supplied with a cure.
According to the experiments by The Overseer, Azoth is not only alive, but just as sentient and chaotic as the Slender Man himself. A gelatinous liquid in its natural state, Azoth thickens into a tough solid form once its exposed to air. Small amounts of Azoth will die when they are removed from a larger portion of it, thus implying there is some sort of internal process that requires an adequate amount of the substance for it to sustain itself. Living Azoth maintains internal fluidity in order to maintain a greater range of movement, while dead Azoth becomes completely hollow on the inside. It is comprised of a large amount of branching carbon chains, which gives it its unique plasticity. These properties allow it to be shaped into objects in both living and deceased forms.
Azoth can also communicate with and locate other pieces of itself via electromagnetic pulses conducted by the metallic particulates within it. These pulses can be disrupted by strong magnetic fields, causing odd behavior and loss of cohesion as well as attraction or repulsion depending on the nature of the field. They are also compatible with neural tissue and electronic devices, causing perception problems in both, along with other possible effects.
Azoth accumulates in the body via exposure to large amounts of it. Its volatile nature produces particulate vapor, which is inhaled and diffuses into the bloodstream via the lungs. It begins to build up in the blood and will then pass through the blood brain barrier and builds up in the amygdale or hippocampus. Exposure to Azoth in this manner provokes an immune response in Runners, the symptoms of which are classified as "Slender Sickness". Constant and increased exposure to Azoth usually causes the sickness to steadily increase in severity over time. The vomiting of Azoth is a common attempt amongst humans to remove all Azoth from the body. In some cases the immune reaction is so severe as to produce anaphylactic shock like symptoms and death on contact with it.
Proxies don't exhibit an immune response towards this substance for unknown reasons, and instead appear to exist symbiotically with Azoth. However, an immune response can be induced via a "cure", after which they will begin exhibiting the standard symptoms. In some canons, Azoth is believed to be some sort of mind control agent that The Slender Man uses to manipulate victims, hence why it appears in the bloodstream of Hallowed Proxies.
The Overseer discovered that Azoth is capable of regeneration, as no matter how many pieces he cut off, the main piece kept reforming into its original size, restoring the lost pieces. It appeared that the only way to discard Azoth was by completely incinerating it, though it was also possible to freeze it into a more solidified form.
As stated above, Azoth is highly volatile in nature and burns in a similar manner to magnesium. The flame can easily be extinguished with a standard CO2 fire extinguisher if sufficiently small in size, as it is not self oxidizing. However, it is almost impossible to extinguish with water until it has been fully consumed. Azoth is also a contact explosive, requiring a threshold of force over a sufficiently small area to detonate. Detonation appears to require gaseous oxygen as Proxies do not explode when struck with it. Ignition will not cause it to detonate for some reason. This explosive force may come from a large amount of triple nitrogen bonds within its chemical structure.
One blogger used this substance to create makeshift molotovs, taking advantage of its otherwise harmful effects.