Sharing my Cel attempt conversation, the last image is lol.
Thinking I may have to talk about paint-by-numbers to setup the starting areas that a Cel can use, then move on from those.
Should have noted this other related topic, my mistake.
In my conversation about Cel animation, ChatGPT mentioned
Note: the generated “transparent” cel images were actually RGB images with a checkerboard background, not true alpha PNGs. I removed the checkerboard by approximation and then composited the layers. That is why some light edge artifacts remain around the fort, fence, and flags.