Hi!

• The real Gameboy supports three 'layers' - Background, Sprites and Window (rules say only background and sprites)
• Each sprite can be 'above' or 'below' the background layer, so you might even say there are four layers (sprites below BG, BG, sprites above BG, window)

Obviously there's more to it (only 10 sprites per horizontal line for example) but that's probably over the top for your jam's purposes :)

@voxel 

*prepares for complex answer*

Your statements are very accurate. However we here at mini jam, would like our participants to have easy to comprehend requirements. We are trying to make an simple, short, and enjoyable experience, rather than focusing on accuracy.

We believe that two layers are easier to understand than three, and since the jam is only 2 days long, well, less is more.

If you wish, you can use more restrictions for your game.