The coldroni /ˈkoʊldroʊni/ is a long stranger with white and blue stripes, narrow eye markings, and a tubular body. Its skin is frigid to the touch, and its blue inner flesh remains slick and oily even in sub-zero temperatures. Accumulation of frost on its surface is typical. The coldroni's lips, gums, and small, evenly spaced teeth are all blue, with the shade ranging from Egyptian blue to almost white in some individuals. Its body cavity contains compacted intestines, the color of which, like its teeth, varies.

The mouth, which lacks a tongue, throat, or any other differentiated oral tissue, connects directly with this internal cavity. The coldroni does not appear capable of opening its jaws under any circumstance, with most individuals' lips being sealed entirely.

The strain's thick skin resists both violent assault and natural wear-and-tear, and although regenerative ability is present, the rate of tissue regrowth is extremely slow (with the stranger requiring several months of dormancy to recover from deep cuts).

The coldroni's internal body temperature ranges anywhere from -58°F in smaller coldroni to as low as -140°F in the largest individuals. It freezes solid in external temperatures of below -147.6°F, but displays no ill effects once thawed out again. This change is sudden, and occurs only at that specific temperature – a coldroni in an environment of 146°F, for example, does not display partial freezing. The coldroni is unaffected by water, although it quickly freezes all water it comes in contact with. If submerged in a body of water, for example, the water around the coldroni freezes to encase its body in solid ice.

Although the coldroni cannot normally be set aflame, all coldroni lose mass gradually when exposed to fire, although the associated symptoms differ per the individual. Approximately 33% display a shriveling of the skin, 32% adopt increasing bodily rictus, and 35% exhibit an excessive shedding of water from their surface. Any decrease in size, however, is still quite slow, requiring several hours of constant exposure to fire to cause any noticeable loss in mass. Large coldroni, in particular, can only reliably be destroyed with the aid of gasoline or other flammable substances.

The coldroni is mute.

The coldroni appears in sub-zero environments. With a tendency towards outdoor areas, the strain's prevalence is greatly increased during winter months, but is not solely limited by climate, as skating rinks, meat lockers, and any other artificially freezing environment serve as suitable hosts to an infestation.

The coldroni grows from a small, thin form, which lengthens and bulks up over the course of several days. During this time, the developing stranger is particularly vulnerable to changes in temperature, and melts away to nothing when its environment is warmed above freezing^୩ conditions.

The coldroni's initial size is based upon temperatures during formation. Coldroni that develop in temperatures of 10°F, for example, grow to about three feet long, while coldroni that develop in temperatures of -40°F are capable of reaching lengths of up to 30 feet. An individual which reaches maturity in temperatures of between 30 and 32°F exhibits nearly no growth during development, and retain a slender, neotenic form. These stunted coldroni are more fast moving than their mature counterparts, and seem to present some level of annoyance to larger individuals, which crush them when they get too close.

The coldroni's disposition is inhospitable and aloof, and regards its surroundings with surly indifference. Just as its initial size is contingent upon conditions during generation, so too does the stranger continue to grow and shrink throughout its life based on ambient temperatures. Low temperatures cause the coldroni to grow larger in size, colder in internal temperature, and more sluggish in its movements, while high external temperatures have the opposite effect.

It spends its life either on the move towards colder temperatures, or at rest once it has reached the coldest point within its environment. It often settles in freezer rooms, on the surface of frozen pools or ponds, or against the windswept sides of buildings, where it lays without moving, its eye markings staring outward, but its attention disengaged. The coldroni is also attracted to abandoned refrigerators, and, once it has found one, curls up inside or around it for several hours before continuing on.

The coldroni also avoids heat, taking wide paths around radiators, fire, and sunny expanses. Smaller individuals even display an aversion to human body heat and the heat radiated from electronics or combustion engines. It is similarly apathetic of most stimuli (when not outright distrustful), and avoids loud sounds or fast-moving objects, from which it stalks away at a leisurely pace.

In spite of these variable conditions, the coldroni tends to grow larger over the course of its life. This rate of growth is almost imperceptibly minute, however, and is only observable over the span of several weeks, with significant growth taking months to achieve.

The stranger's presence causes a sensitive to experience a sudden drop in body temperature, with larger coldroni causing a stronger effect. This effect occurs regardless of how well-bundled the sensitive is, and grows more severe over time. Frostbite generally sets in after 20-46 minutes of exposure, with death from heat loss after several hours.