A Farce to Be Reckoned With — Roger Zelazny; Robert Sheckley

On a devilish sabbatical in Europe, Azzie discovers that morality plays are all the rage. He decides to strike back by producing an "immorality play", in which seven nondescript human pilgrims will be allowed by magic to attain their hearts' desires. But the forces of Good are determined to close the play before it opens. New characters suddenly start roaming the stage, such as a Grateful Dead-listening Cyclops, and Azzie's own protagonists begin changing their hearts' desires on the slightest whim. This is one theatrical production that could do without an angel - and there's even worse news waiting in the wings...