Each Subterranean Pet hosts at least one of several species of symbiotic fungus, and many also tend to sprout crystalline growths along their skin. The fungus provides illumination in the tunnels, and both it and the crystals are highly sought-after for their use in scrying and earth magics. It is thought that, as they explored the tunnels and caverns that would become their home, the forebears of the modern Subterranean Pets were drawn to the light produced by the lichen, and, in either rolling around or resting in the plant, allowed it to take root on their backs. The cause of the crystalline growths is a topic of fervent debate in Subetian academia. A mixture of the lichen's spores and powdered crystal was eventually used to develop Subterranean Potions and Elixirs, and these Pets can now be found all across Subeta.

However, even while Subterranean Pets spread across the globe, they still maintain a close bond with the undead community. Shadowglen remains home to the largest population of Subterranean Pets to this day. Over half of that group resides in or near the zombie village, and it's not uncommon for resident zombies to leave their doors or tent-flaps propped open throughout the night to allow curious Subterranean Pets to wander in. Many have at least one corner piled high with pillows and blankets for such visitors to 'burrow' into. Although the Subterranean Pets' reluctance to leave the area can be attributed in part to the ideal conditions of Shadowglen—the constantly-dim lighting, the myriad caves and tunnels, and the moist atmosphere perfect for many varieties of fungus—it is clear to any visitor to the Zombie enclave that there is a true affection between the Subterranean Pets and the undead who welcomed them back into the outside world.

The rest of Shadowglen's inhabitants have also welcomed their newest neighbors—they love anything that they can spin a good spooky story out of. A few Shadowglen residents have started pranking tourists, telling them tales of glowing will-o-wisps waiting in the dark to lead them astray, and then offering them guided tours of the local highlights—and then, when the tourist turns their back, the guides stuff their pockets with the roots and insects adored by Subterranean Pets, ensuring a surprise addition to their group, the new arrivals often initially seeming to the tourists to be nothing more than floating balls of blue light, like the will-o-wisps of the story. Fortunately, most tourists who visit Shadowglen come prepared with a good sense of humor.

As Subterranean Pets have become more and more a part of daily life on subeta, a trend has popped up for their owners to try and cultivate the fungus in elaborate patterns; forming glowing pictures, words, or abstract swirls. A good pet owner should always be aware of the health of the lichen, as it can be a good indicator of the emotional state of their host. If you notice the mushrooms on your Subterranean Telenine are looking a bit dim, that may be a sign that you should put aside a bit more time every day to play with them!