The make command was crashing with the following error
rgbgfx -d1 -o gfx/minimized_mon_sprite.1bpp gfx/minimized_mon_sprite.png FATAL: Image height (5 pixels) is not a multiple of 8! Conversion aborted after 1 error
just asked around in the pokered discord. Turns out that rgbgfx got a total rewrite in v0.6.0, so it wont take any png that isn't in 8x8 tile dimensions.
They provided an alternative 8x8 png that allowed the .gbc to compile.
Thanks, but there's more to it than just replacing the PNG. (Note that the ROM changes when you do that, and the in-game graphic looks wrong.) You can use an older version of rgbds in a folder named rgbds.
The make command was crashing with the following error
rgbgfx -d1 -o gfx/minimized_mon_sprite.1bpp gfx/minimized_mon_sprite.png FATAL: Image height (5 pixels) is not a multiple of 8! Conversion aborted after 1 error
A quick google leads to: https://www.pokecommunity.com/showthread.php?p=10607889
Where it's stated by jojobear13
They provided an alternative 8x8 png that allowed the .gbc to compile.