In the era of Perenia in which the Tyranny of Mundanity campaign takes place, magic is running rampant and new, mystical creatures are springing up all over the world. One such creature, encountered by the party in a later form, is the Shadow Thief. These creatures spring from dark magic, lurking in shadows from which they are born. A shadow thief’s birth requires a confluence of magical energy and a strong contrast between light and dark, usually shadows cast by a high sun.
Because of their extreme vulnerability to light, few manage to survive the shift of shadows as the sun moves. Now, however, with magic prevalent as it is, millions are spawning every day, and some survive to gain enough strength to withstand even direct sunlight and become formidable hunters.
Their growth is slow and predicated on feeding upon the shadows of living things. As they grow, they can take upon themselves the powers of things they consume. They of course begin small, nibbling on the shadows of creatures entering and leaving their shadow of residence. As time goes on, they are able to consume whole shadows, often driving the shadowless victim mad in the process.
Eventually, though capable of braving the sun, they rankle at its itching annoyance and seek to build a dark home to guard them from the light. This home takes many forms, built by delivering the shadows, and usually their owners, to it as an offering. They will seek large shadows to deliver still alive to the nest where they can feed it long term.
Their nests are dark and labyrinthine with a confounding magic to them. Those who do not escape quickly will go mad and starve while feeding the shadow.