I've got the idea of trying to make Scratch render the GameBoy's VRAM on screen, so this will render BG0, BG1 or just the tileset.
Scratch is very slow so SHIFT click the green flag to turn on turbo mode.
If you select the BG rendering method it will ask you to specify a tileset bank to use. since OAM uses bank 0 you might want to use bank 1 this time.
This project will NOT render OAM on screen.
I've loaded up a VRAM dump from Pokémon Blue (German Release) from my own GameBoy Color emulator written in C# and I've dumped the ROM myself using an Arduino microcontroller, and yes I do own the game too.
The memory dump starts at 0x8000 in the emulator so if you want to try and make your own dump you'll have to find a way to dump VRAM on an emulator, keep in mind, the first value in the dump must be the byte at 0x8000. The dump must contain 10240 values, 8192 (8KB) values go into tileset RAM and the rest is the BG Map RAM which is 32 x 32 x 2 bytes since it has 2 banks.
Feel free to explore the project to see how it works.
If you enable the viewing of the variables you'll be able to see how the data is being processed.