So right now bank 3 is 48% free. Which is, due to changing circumstances, where I have to put the rest of the game. I will cram as many levels as I possibly can in this bank and then put the ending and Easter egg in bank 2. So here's how GoSub GB is shaping up:

1. bank 0 - main game "engine"
2. bank 1 - data for levels 1-25
3. bank 2 - ending, Easter egg
4. bank 3 - data for levels 26-end

I have a small amount of room left in banks 0 and 1. I can't put it in bank 2 because the music won't work since it's in bank 3. I am pointing the second half to bank 3 to play the music so I can't put it in bank 2.

I put the latest ROM on my Game Boy and it works fine so far.