The Pcs discover an ancient, dusty oil lamp, somewhere in the bowels of a dungeon. Naturally they "rub it", and out pops a wizened, old djinn. So far so good. Then it speaks...
"Ah at last, at last I am free! Now grant me my wish!"
When the PCs explain that they are the ones that should be granted a wish, the malignant djinn explains to them that his particular oil-lamp has a curse placed upon it. Whomsoever releases the entity inside shall be geased to grant the djinn's wish to the best of their ability.
Groans ensue from the party. The djinn rubs his wrinkled hands, grins, and proceeds to name his wish. What could it be?