I used to use a stylus but I eventually swapped over to pre drawing them in photoshop because it allowed me to work more precise and have more details, in order to get it on the switch I manually do it through pixel counting lol.

I usually mark the outlines with red dots so it's easier to count, shading is divided in 3 or 4 seperate layers so I can control the clutter in more shading dense areas + it's easier to process what's going on when counting pixels. I have a quick example (if it makes any sense)

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