There are a few things worth talking about as you make your way through the last couple of pages of this book. The concepts of cross-platform considerations, plugins, and attribution are covered in this section.
You can create multiplayer games and have users on Android and iOS devices playing with or against one another. To accomplish this, you can use something such as Google Play's games services.
Another consideration is the various screen sizes of mobile devices. Apple has a finite number of mobile devices using iOS, but Android runs on a lot more different screen sizes and resolutions. You do not have to create one version for every screen size. Instead, you'll need to consider relative layouts and flexible dimensions.
As always, test your game on as many different devices as you can and be sure to vary operating system versions, screen sizes, and screen resolutions. In absence of actual hardware for testing, use software emulators.