The Spellplague broke out in 1385 DR (the Year of Blue Fire), caused by the release of wild magic from the death of the goddess Mystra. Entire countries are gone, especially South of the Sea of Fallen Stars. Familiar lands have become magical. Earthmotes (islands of rock) float through the skies. Strange towers of stone jut from the surface. Spectacular waterfalls and chasms formed from Underdark collapses are common. A huge opening into the Underdark has formed south of the Chondalwood. The spellplague affected anything it could reach. Even some ancient realms returned to Toril from the Feywild.
Plaguelands are areas where remnants of the Spellplague continue to affect the land.
Spellscarred creatures have been affected by the Plaguelands and have been physically marked by this encounter. They have been granted unique abilities, but at a price.
Plaguechanged creatures were altered by the original Spellplague. There are very few of these monstrosities, and even fewer are free-willed and mobile, but all of them posses frightening abilities.