The Incredible Hulk #169

The Harpy is flying off with the Hulk when they are both sucked up into a powerful tornado. They find themselves on a floating city and are confronted by its only inhabitant, the Bi-Beast. In the thin atmosphere, the Hulk transforms into Bruce and the Bi-Beast commands him to repair the city's broken down machinery. Instead, he uses the devices he finds to try and turn the Harpy back into Betty. M.O.D.O.K. arrives, takes down the Bi-Beast and decides to claim the city as his own. The Bi-Beast resists and sets the self-destruct. The Harpy turns back into Betty just as the city explodes.