Hi, How do you get one background to be transparent through another on the GBA? I know you have to set bits in REG_BLDMOD register but I don''t know which ones. How does the GBA know which pixels should be transparent? Is it palette entry 0? Thanks for any help, Hamish

Yep use palette index 0 for the bits you want transparent With 16 colour backgrounds you have 16 transparent colours (one in each of the 16 palettes).