Geological / environmental event
A wave of purple-gray shadow rapidly creeps from the center of Molaesmyr to engulf the city and, eventually, the entire Veluthil Forest.
A thousand years ago, the great brumestone-powered floating city of Aeor was home to a thousand incredible arcane experiments as creative as their inventors. One such team of arcane researchers wanted to create a self-replicating source of spell components, like an endless supply of residuum. To this end, they attempted to birth a species of plants that would provide arcane assistance similar to that of residuum while simultaneously breeding and expanding to eventually cover the world. At that point, the mages reasoned, everyone could access magic and mankind would no longer rely on the gods for protection—or anything else, for that matter. Although it took failure after failure, the team gradually began to approach their goal. When Aeor fell, a chunk of this technology fell into the Veluthil Forest. The elves of Molaesmyr had trusted Corellon the Archeart to guide and protect them since the dawn of their civilization. However, during the Calamity, Molaesmyr came under attack and the Archeart did not answer her call for help. Fearing for their lives, the elves threw up magical protections around their city and fled to the Feywild. There they made a pact with the queen of the Summer Court: so long as one of her eladrin ruled Molaesmyr, the magic of the Summer Court would guard the city from destruction. Thus protected, the elves returned to Wildemount. Exandria was a much different place than they had left it. After the Divergence, most of Wildemount lay in smoldering ruins, its peoples scattered and its civilizations lost. The elves' barriers had failed, leaving Molaesmyr to grow over with wild plants and predators in their absence. With the help of the Summer Court, the elves began to rebuild their home. In 583 P.D., Molaesmyrian druids noticed an unnatural disease slowly creeping through the flora of the Veluthil Forest. Further investigation uncovered a piece of experimental Aeorian technology. Like so many of its predecessorss, this experiment had failed: instead of creating magical plants, it corrupted all nature with which it came in contact. The royal advisors recommended asking the Summer Court for help, but the common people, remembering how their god had apparently abandoned them only centuries before, desperately feared another betrayal. While government representatives sought fey aid, more scientifically minded elves investigated the technology further. About a hundred years prior, the eladrin queen had an affair with a member of the royal advisory council and bore a son, whom she named Galrion Talviel. Afraid of the political repercussions should the child's lineage be exposed, the lovers broke off their relationship. In 585 P.D., several things happened in very quick succession. First, tired of being forced into politics when all she wanted to do with her life was guard the Material Plane from extraplanar monsters, the eladrin princess renounced her claim to the Molaesmyr throne. Her younger brother Galrion would take her place as heir, unwittingly breaking the city's pact with the Summer Court. Second, Molaesmyrian mages accidentally activated the artifact's full potential, releasing a blast of arcane corruption that killed thousands of elves and poisoned the Veluthil Forest, transforming it into what modern visitors know as the Savalirwood. The king and queen perished, but not before their children and several thousand refugees escaped. Galrion went on to become king of Uthodurn alongside the queen of the dwarves, while his sister, uninterested in politics, traveled south to slay monsters. Eventually, Galrion's son, Imathan Talviel, became king of Uthodurn. However, because Galrion was a bastard high elf, Imathan is not the rightful ruler of Molaesmyr according to the pact with the Summer Court. Until Galrion's sister or her eladrin heir claim their rightful place, the children of that city can never return home. If they try, terrible horrors will emerge from the darkness to claim their lives and they will forever haunt the ruins. The trees aren't the curse, but most believe they are and are convinced that curing the corruption will save Molaesmyr. In reality, the magic of the Summer Court may be able to protect the city, but until the heir is restored to the throne that magic remains unaccessible to Molaesmyr. Worse, who said anything about the heir wanting to come back?