Oazduke's Vengeful Head.
The head haunts all headsman and executioners.
A floating, bloody head, long separated from its body, is a particular legend among a very particular group of people, executioners, specifically those that chop heads from a block for a living. It was that infamous highway robber, Oazduke the Vengeful, who when finally captured and put to the axe, screamed his foul hex, seconds before his head flew off.
"You will know it is me when I'm through
A curse on your ilk and on you!
May my severed head haunt you eternal
Frightening you headsmen infernal!"
Years later, not one but two(!) weary, puffy-eyed, spooked, headsmen, haunted day and night by Oazduke's insufferable severed head, approach the party cleric in order to hire him to exorcise the ghost head once and for all.
A PC Conjurer or summoner, basically any mage whose sole purpose in life is summoning creatures to aid in battles and various situations, is cursed with a hex, and needs to find a way to undo the curse...before he goes mad, or his fellow PCs throw him out of the party, or worse.
Everything he/she summons, never goes away. So you'll have to figure out what the heck to do with that dire bear or fire elemental once it's done fighting the orcs for you. Eventually a caravan of bizarre creatures either annoyingly ends up following the summoner around, or they go off to cause mayhem elsewhere. Bad news for the poor spell-caster regardless.
One day a a wind begins to blow out of the West. The next day it gets stronger. And stronger still the next few days. Eventually (and fortunately), the speed of the wind tops out at a steady fifty miles an hour, but continues to blow. Soon an entire kingdom is wondering why it's not abating. The weather mages deem it unnatural but can't seem to banish or control it. The priests of various faiths claim it's divine. The End-Of-Days crowd is having a field day with their predictions of doom. No one knows why the gale persists. When inquiring with neighboring kingdoms, it seems they too suffer from a persistent western mistral. Eventually the populace begins to adapt to living with a twenty four hour a day wind. Always from the West, and perpetual. What could be causing this? A raging Elemental king? a curse from the gods? an unearthed artifact? Or has Nature itself gone haywire?
Magic should have side effects, both expected and unexpected - fortuitous and deplorable. Expected side effects add anticipation, while unexpected ones increase the drama of the scene. The result can be comedic or dire, it dpends on which circumstances work best for your game.