The Lightless Cyst is an area of deep darkness where the light of ghostly lichens only functions if the area's master is away on business. This master is the magical staff Eldacil's Vine. When this sentient item is home, buried in the pulsating mass of a colossal-sized ooze, it keeps the area in darkness so deep that only those of advanced sight can make their way around. It does this because the hill-sized mound of goo that it inhabits, was once the body of the demon lord Juiblex. One of the favored attacks of this sickly ooze demon was lurking in an area of impenetrable darkness, savoring the panic of those that could not see into it.
Late in the Demon Spawn War, the Covenant general Melrith cornered Juiblex in a long unnamed cavern. In the ensuing fight, hundreds of twig blights charged upon Juiblex, throwing their bodies into certain doom. Hiding among the charging soldiers was Melrith and a staff designed to re-balance the Energy Composition of others. Melrith, distant from Covenant operations for the past decade, a product of the growing darkness inside her, boldly took on Juiblex alone. Luckily she had enough body shields around her to take most of the blows. Melrith succeeded in driving Eldacil's Vine into Juiblex. The power staff devoured the demon's energies, but like four times before in the Demon Spawn War, the body was killed, but the mind escaped.
Melrith could not believe the amount of energy the staff absorbed. She had a telepathic link with the weapon, but could not reach it. Next to the battle, she had set the staff's many faceted tip to Dark Nature Energy. She had hoped to use whatever energy the staff absorbed in her experiments. Melrith was never able to retrieve the staff. The caustic juices of Juiblex body kept her away. This was unusual because in previous kills, Juiblex's body would go into demoniac death throes. Forced to leave the Mortal Systems in the Angelic Departure (9494 GE - 9500 GE), Melrith left Eldacil's Vine in a still-living blob; Juiblex's 7th Incarnation. Many years later, Melrith learned that it was the staff's sentience, Eldacil, that was keeping the body alive. The goodly nature of Eldacil was such that she did not like taking lives, so she kept the unthinking mass alive by feeding it. Somewhere during this process, the Dark Nature Energy the staff was holding, an enormous amount give that Juiblex was a demon lord, corrupted the staff. Not so good anymore, Eldacil used one of the pseudopod of Juiblex's 7th Incarnation to turn the staff's facet to an empty slot. This begin the release of the staff's energy into the area around it.
In the next age, the Lith-Crillion Era, the staff and mound grew to be one. Using Juiblex's stolen energies, nearly all converted Dark Nature Energy, the staff went to work spreading a vast root system outward. This corrupted Underdark fey in the process. Myconids, shriekers, and any other subterranean plant-life that came within range had their Nature Energy replaced by its antithesis. Some of this made it to the surface, bolstering the Dark Nature of Emeldimir's three blighted forests.
Near the center of the Lightless Cyst is a vine covered hill that still pulsates. This mound is Juiblex's 7th Incarnation. It and the staff are responsible for making Velkyn's northeastern reaches a place of Dark Nature.
Even though Juiblex has no connection with its old body, oozes, slime and puddings are attracted to this area.