The Spellplague

The Spellplague, also known as the Blue Breath of Change, was a disaster that struck the entire realm and affected even the planes themselves. It was caused by the assassination of Mystra at the hands of Cyric and Shar. It continued for a decade, leading to the Wailing Years during which arcane magic became dangerous and unpredictable, killing many mages due to magic-related illnesses or horrible arcane accidents. Magic items were disrupted, and the planet Terrix was forced to adapt and recover until magic became what it is today.