The Curse was an evil spell cast by the great wizard Megaboz.
Lord Dimwit Flathead the Excessive's new statue of Fublio Valley darkened the wizard's dwelling. In 14th Mumberbur 779 GUE he appeared amidst a cloud of smoke in the Castle during a grand feast and cast the Curse against Dimwit's life, family, and Empire:
Frobnitz! Frobnosia! Prob Fset Cond! Zmeqb Intbl Foo!
In only a few moments, this killed Dimwit Flathead as well as the Twelve Flatheads to a sudden death. The court magicians were able to postpone the other effects of Megaboz's Curse for quite some time. Some people reacted in weird ways: a crackpot religion begun known as the Inquisition, believing that by executing all the people of the Empire, the Curse would be forestalled. Wurb Flathead offered half the Empire's wealth to anyone who could stop the Curse.
Eventually, the same day in 883 GUE, the Curse brought about the collapse of the Empire and the destruction of Flatheadia.
The anniversary of that event was commemorated as the Curse Day