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I think the last one is probably the best out of these as far as coloring goes. I don't know what kind of markers you're using, but I'm not sure how much I like being able to see the marker strokes that heavily on the first two, especially on the second one where you can see where the strokes overlap in the sky. Instead of looking intentionally scribbly, it just looks rushed.

If you can find a way to blend the colors together more like you did on that last one, it'll look better. That's kind of my personal preference, though. I think the scribbly, messy look works depending on what you're going for, but with the kind of stuff you're doing it doesn't seem to go together as well.

Except for the mermaid. That mermaid is cool.