The merridronel /mɛrədroʊˈnɛl/ is a small, blue stranger with short limbs and a wobbly, tubular, liquid-filled^Ƅ body, the surface of which is not wet, but is difficult to hold onto. Its skin is composed of a single piece of thin, stretchy rubber. The merridronel lacks an inner mouth, and its expression curves up into a fixed smile; the lips, like its toes, are fused.

The merridronel's presence is accompanied by random but melodic notes, similar in quality and resonance to the jingly sounds of a child's jack-in-the-box or otherwise, quietly "musical" toy.

The merridronel can be found in damp or humid interiors of all kinds. There, it starts off as a small, rubbery bead that swells to form the mature merridronel within six seconds.

Infestations always begin with a single individual; this "qualifying merridronel" splits itself laterally into two "new" individuals, which continue to duplicate in an amoeba-like manner. The duplication rate varies based upon the number of people nearby; in areas of high population density, duplication occurs once every 50-180 seconds whereas, such a split occurs every 3-10 seconds in depopulated areas.

The merridronel cannot grow to completion in overly dry locations. In such unsuitable locales, it generates instead as a moist, crumpled husk upon the ground, leaving behind the smell of burnt rubber as it dessicates itself fully, and crumbles apart.

Despite the stranger's lack of coordination, it tends to stay near its companions, and groups tend not to spread themselves too thin. When left to expand, regardless of the space, the mass of merridronel to pile up on top of one another, and the collective weight pops those at the bottom. A group's size thus tends to stabilize after a certain point.

Though lightweight and non-destructive, the merridronel's spread can pose a hazard to easily toppled objects,^რ just as its gel can soak into a carpet or a discarded jacket to cause a mild discoloration.

The presence of sensitives does not alter a merridronel's actions in any way, and it can be picked up as long as care is taken not to puncture its skin. When held, the stranger continues to wiggle, oblivious to its captivity. Those sensitives who wish to spend time with the harmless stranger, but do not wish to risk breaking it, may lie down on the floor near a group – they will inevitably find themselves covered in a tumbling pile of merridronel.

Touching a merridronel alters its ability to duplicate itself.

Infestations of merridronel are short-lived, and their longevity as a group is determined by the initial, "qualifying" merridronel's lifespan. Though their death (whether deliberate or otherwise) does not harm the group, once their lifespan has elapsed, individuals begin to pop spontaneously, and the group dies off within thirty to seventy seconds. The burst merridronel's skin dries and shrinks over the course of several hours, while its gel evaporates within twelve to nineteen minutes.

Infestations often appear in direct succession, in specific locations whose properties support the strain's recurring generation (such as humid locker rooms and damp basements). The gel inside the corpse does not evaporate in the presence of immediately subsequent merridronel, allowing their gleeful "victory splash" to be observed.