So I got some help on my Game Boy version of Hamburgers En Route To Switzerland. It now works again. I originally made it not work after attempting to add a boss screen where you shoot at the boss.
I had to change the background from light gray to white. I had to turn off the display for a few frames, and I made it white to make it look less shocking and more smooth when the boss milkshake disappears. Sad, because I liked the way it was, but oh well. I'll do just about anything to make this work again since I have put so much effort into it.
Since the milkshake's cream on top was the same color, I decided to make the cream light gray instead. I had to make the milkshake thinner in order to make it fit within my self-imposed tile limit for it.
What I am going to do next is add a boss defeated tune. I'll have to put it in bank 1 since bank 0 is 97% filled up now. I had to get the ending out of bank 0. I'll put it in bank 3. So there is hardly any room to make any drastic changes to the game. And then after that if nothing breaks, add some more music to levels 2-6. And, if nothing else still breaks, add 2 more levels if I have enough room for their music data. I should have enough room if I begin using bank 3 since it's empty right now.
All this talk about burgers is making me want one. Or a milkshake. A nice strawberry milkshake. Burger King stopped serving strawberry milkshakes. I don't know why people like vanilla. It's evil.