Curse of Strahd
In the Year of Blue Fire (1385 DR), a magical disaster called the Spellplague changed the face of Toril, its lost sibling Abeir, and even the planes themselves. Flesh, stone, magic, space, and perhaps even the flow of time were infected and changed. Most scholars believe that the Spellplague was the direct result of the murder of the goddess Mystra at the hands of Cyric, which Shar engineered. This popular theory holds that magic was bound so long in Mystra’s Weave that, when the goddess died, it spontaneously and ruinously burst its bonds. Areas of wild magic, already outside the constraints of the Weave, touched off first, but the plague raged on and on in ever-widening spirals, devastating some places and leaving others untouched. It even tore through the realms of demons, gods, and lost souls before the end.
Ancient realms that had passed beyond easy reach of the world were pulled back, such as the Feywild (called Faerie in ancient days). The Abyss, home of demons, fell through the planes, unleashing swarming evil before finding its new home at the bottom of the Elemental Chaos. Even the long-forgotten sibling world Abeir burned in the plague of magic, despite having been cut off from Toril for tens of millennia. Portions of Abeir’s landscape were transposed with areas of Toril in the disaster. Such landscapes included their living populations, bringing realms such as Akanûl and Tymanther to Faerûn’s face. Across the Trackless Sea, an entire continent of the lost world reappeared.
The Spellplague was a potent agent of change, but it also set off a whole string of secondary catastrophes.
The Spellplague ate through stone and earth as readily as flesh and magic. Broad portions of the continent of Faerûn collapsed into the Underdark, partially draining the Sea of Fallen Stars into the Glimmersea far below and leaving behind a gigantic pit called the Underchasm. The event splintered the Old Empires south of the drained sea into a wildscape of towering mesas, bottomless ravines, and cloud-scraping spires.
Of those ancient lands, the most changed by the Spellplague were Mulhorand, Unther, and Chondath, as well as portions of Aglarond, the shores of the Sea of Fallen Stars, and the Shaar. What was once called Halruaa was destroyed in a great holocaust, as if every spell held there had loosed its power simultaneously. The land bridge between Chult and the Shining South was sunk; now only a scattered archipelago remains.
Tendrils of the Spellplague reached to many other corners of Toril, sometimes bypassing great swaths of land by infecting both sides of the many portals that dotted the world. Such an effect might have been responsible for drawing portions of lost Abeir into Toril. Some sages suggest that the two worlds have undergone periodic conjunctions ever since they diverged, but that these were too subtle for most creatures to notice. By an accident of timing, the Spellplague occurred during just such a conjunction, which caused the briefly overlapping lands to run athwart each other instead of passing in the night as before.
Pockets of active Spellplague still exist today, most notoriously in the Plaguewrought Land. Each of these plaguelands is strange and dangerous. No two possess the exact same landscape or features, but entering any of them could lead to infection by the Spellplague. Luckily for the world, the remaining plaguelands possess only a small fraction of the Spellplague’s initial vigor and are in hard-to-reach locales, often surrounded by twisted devastation. Most lands of Faerûn and Returned Abeir are entirely free of such pockets, though the plaguechanged and spellscarred might appear in any land.