Faerzress is a magical radiation only found in the Underdark, a remnant of High Magic that helped shape the Underdark itself. It interferes with the casting of teleportation and divination spells.
Areas of high faerzress concentration can manifest physical signals, ranging from subtle shifts in temperature to visibly glowing rock formations.
Etymology
The word faerzress is composed of faer (magic) and Z’ress (to hold dominance or to remain in force), which together mean magic that remained. However, its original term had faer and Z’ress inverted, which rendered the term as dominating magic. That older composition was much more telling about the primary task of these emanations: to keep the drow in the Underdark (faerzress exerts a calling effect on drow).
Effects on magic
Faerzress can affect magic and spellcasting in unpredictable ways, in some ways like wild magic. Although the knowledge of faerzress among surface-dwellers is sparse, it is known to mainly affect divination and conjuration spells, making teleporting by magic in the Underdark a risky effort.
Some areas in the Underdark have stronger faerzress emanations than others. It is possible to enact rituals to alter the concentration of faerzress in an area or to affect a pocket of it, although such spells often attract unwanted attention from denizens of the Underdark attuned to the faerzress.
Effects on plant life
Since the Underdark lacks food or light for plant life and fungi, many plants and fungi that are found underground find ways to live on a diet of faerzress. It is the sole food source of a plant-like life form called magivores, which can serve as a food source for Underdark settlements.