Okay...my initial thought is a short campaign that utterly shatters the 4th wall. The characters know from the beginning that they are characters in a game (this will give them some unique abilities) and are setting out to free themselves from the control of their players. For extra silliness, races would include Muppetborn, Toonkind, Toys, a variety of sentient animals, and maybe Clowns, some Pokemon, and perhaps some odd D&D races, like flumphs and mimics. I'd be making this up as I go, so expect lots of unpredictability, pop culture references, and assorted nonsense.
Too silly or let's do it?