While I agree with the bit about our synergy, AFAWK only the one god is associated with cold and death.
A species of fungus derived from the fungus used in fungus spawn. It is capable of surviving in the form of a single cell, as well as surviving dormant under a protective coating (as many real-life organisms do). Its most notable attribute is its behavior when in a warm, damp, and dark area, such as the inside of a human body. It feeds off of heat and expands into a colonial organism. As it grows, it engulfs, breaks down, and replaces various inner organs. During this period, the host shows no outward signs of infection aside from chilliness and slightly increased hunger. As the mass of fungus in the host increases, certain structures begin to form, including "ganglia" which coordinate infection and pods which may be primed to explode at the desire of the colony. Once the ganglia have developed to a point where they can intelligently direct the infection (typically a week or two), the infection begins to approach the host's central nervous system. During this time, the subject may experience itchiness. Once infection of the central nervous system is complete (typically within 3-4 days of the start of central nervous system infection), the ganglia and organism as a whole have control over the host and be capable of replicating the host perfectly (by essentially converting the neurons' patterns into ganglia patterns, or in thaumotalogical terms converts the host's mind into a Fungus Sleeper mind). Once this stage of infection is reached, more aggressive infection begins. While the outer epithelium and subcutaneous tissues (aka the outer part of the body) are mostly untouched, as are the blood vessels and sanguinous fluid itself (allowing the Sleepers to bleed blood), the rest of the body is replaced by fungus replicating the functions of the body. By the time infection has completed to this stage, the "host" will usually manifest superhuman strength, toughness, speed, and agility (although these are typically hidden to maintain the illusion of being the original person), as well as various organs such as the aforementioned explosive pods and perhaps some other fungological weapons (e.g, a "cannon" launching smaller explosive pods or a thorny whip similar to Tiberius's or something).
At all points from when the first ganglia develop, the behavior of the fungus in the Fungus Sleeper may be influenced by Donut. He may direct the infection to slow down or even stop, develop more or fewer explosive pods, influence the other organs being developed, etc. This influence may expand to actual commands once a certain concentration of ganglia is reached (which, due to the ganglia density in the former central nervous system, is normally around when the host is overtaken by the fungus). It is inadvisable that these commands reveal the presence of the fungus unless necessary.
The fungus spreads in several ways. Most notably is the explosive pods, which contain a combination of explosive chemicals allowing the pod to explode, sharp fragments of tissue, and spores. When consciously detonated, or upon the death of the fungus, the explosive chemicals intermix, causing an explosion which causes injury and infection among all within the blast radius. Other methods include the smaller explosive pods, spores which hibernate in the excrement of hosts, spores found in the saliva and other bodily fluids of hosts, and even spores which are spread in the lungs of the hosts once the infection reaches the lungs. These spores will infect upon contact, inhalation, or accidental ingestion. These qualities allow slow spread throughout a community covertly or more rapid infection through combat. The spores themselves are tough: they are sufficiently dormant to technically not be alive until they infect a host, rendering them immune to most death magic; the spores are unaffected by most extremes of temperature (similar to the dormant forms of many RL microbes); they require zero sustenance; and the spores can hide in soil or waste pits, being passively absorbed but undigested by various plants or animals until a human being ingests the spore. A single spore is sufficient to begin the infection.
Spoilered for length.