The Incredible Hulk #169 (1973)

“Calamity In the Clouds!” Written by Steve Englehart, pencils by Herb Trimpe, inks by Jack Abel. Cover art by Herb Trimpe. The Harpy is flying off with the Hulk when they discovern 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, but the Bi-Beast resists and sets the self-destruct. The Harpy turns back into Betty just as the city explodes

Key book; first appearance of the Bi-Beast.  Good/very good condition.