Felthren-dro-Dlenruksurd is the name given to a theorized mass extinction event that took place throughout the planet Mioura between approximately -6400 CGC and -6000 CGC. It is also known as Garl, a euphemism also found in Miouran records referring to the event. Prior to the Watershed in 4100 CGC, it was sometimes only called "the precursor mass extinction event" for its perceived uniqueness in history; the near-annihilation of the species in the Watershed has resulted in more historians and archaeologists using the term Felthren-dro-Dlenruksurd to distinguish between the two events. As with the Watershed, there were few surviving precursors once the apocalyptic event concluded, but there is evidence suggesting that, unlike with the lead-up to the Watershed, the precursors of ancient Mioura were aware of the impending apocalypse and sought to avert it or at least mitigate its effects on their people and world.
Felthren-dro-Dlenruksurd itself is broadly understood to have been the end of Miouran antiquity and the precursor species' undisputed reign over their native planet, as the only survivors of Felthren-dro-Dlenruksurd were those places into a sleeping stasis called al-Kerl and the countless generations of caretakers and guardians that watched over them. These scant few survivors were unable to build up any meaningful settlements above ground, as animated stone statues — originally called dlenruk by the precursors and eventually known as colossi to the rest of Ealdremen — rampaged across what remained of Mioura.
Etymology
Dlenruksurd can be broken down into the components of "god," "you," and "kill". The Shekzardic name for the colossi, dlenruk, derives from these same base words and was in use during this period, but it is not known if the event was named for the colossi or if the colossi came to bear the apocalyptic event's name themselves.
Felthren is a word used throughout Miouran antiquity to denote eras or periods of history, such as reigns of particular monarchs or unbroken years of peace. Because this word tends to refer to lengthy eras rather than singular events, it is believed that the "event" of Felthren-dro-Dlenruksurd was not something that happened in an instant, but was something foreseen and gradual that nonetheless could not be prevented, and this incremental decay lasted long enough for the era to be named as such before it ended. This is further corroborated by records mentioning the event seeming to, at times, be separated by hundreds of years. Documents that seem to be older tend to speak of the event as a coming storm or even as something that might be reversed entirely through the colossi. On the other hand, accounts from the end of this era paint the image of a desolate world beset by creeping entropy — nothing would grow, nothing would remain whole, and nothing would survive.
Garl
The "alternative" name for Felthren-dro-Dlenruksurd, Garl, has no clear origin. Recovered and translated records from different Miouran cultures have used this word in relation to Felthren-dro-Dlenruksurd, even if they seemed to have their own native term for the extinction event that Shekzardic called Felthren-dro-Dlenruksurd. When translation attempts using spells are made upon any record bearing that language's rendition of the word Garl, the spell appears to struggle and fail to produce a word even if it works as expected on other words or letters in the same document. Instead of a word, would-be translators of Garl feel an out-of-body, dissociative emptiness. Garl is sometimes translated as "void" or "hollow" because of this phenomenon.
ZGN
A solitary scroll recovered from the antiquated nation of Rethnald, known for its widespread cultural emphasis on the concept of "true names" and identity, has a unique epithet that appears to connect to the planet-wide understanding of Felthren-dro-Dlenruksurd. Rather than use a word, however, the scroll referred to the state of the world with three characters translated as ZGN. Because of the Rethite linguistic tendency wherein they avoided using words that even sounded similar to a taboo subject, it is supposed that ZGN is an intentionally-meaningless epithet, unpronounceable so that it could never be named in speech even by accident.