16 x 16 challenges
A long, long time ago, 16*16 pixels was what you'd get to draw a digital icon. The Lego lettpress bird designs are essentially made at the same resolution: built on a 16x16 baseplate.
One big difference is that a single point in this grid can be filled with more than a full square 'pixel'. There's dots, shields, quarter circles, thin lines and other more custom shapes that can be placed within this 16 point grid. These other shapes leave parts of the pixel-area open, thus creating additional shapes (negative space). Printing in multiple layers allows for even more variations. Similar to the different kinds of path operations in vector drawing programs.
Path operations in Inkscape
I could never confidently imagine the result of those actions, always had to try a couple to achieve the desired result.
I'm getting better at it with the manual approach using LEGO stamps, but this really is the part where the mindf*ck happens. Most design details need multiple tests to get things right, especially because the order of printing is a deciding factor.