It took a couple of hours, but I finally made the milkshakes shoot onion rings. Just like in the Game Gear versions, the vanilla ones always shoot, the chocolate ones shoot sometimes and the strawberry ones never shoot. I also added a bunch of new sound effects and other minor changes as well, like adding more clouds. It's amazing though that I can fit all this into just 24KB. What if I need to make it bigger? Will it just automatically grow bigger or do I have to do something? I'm using C and cc65 to make this.
I'd love to learn how to make the background scroll, but since hardly anyone seems to care about this project, it will probably just remain static as it is right now. But it will change from time to time. Level 2 I want to be an underwater scene, for instance. The vanilla milkshake had to be a light gray, but I think it turned out good. And all the sprites can be at the same y position with no flicker. There are 8 sprites in the game: 4 for the burger, 2 for the milkshake, one for the fry and one for the onion ring. So it worked out just perfectly, since I think the limit is 8 characters at the same y position with no flicker.