His advice was to sort out the tones in the image first. Tone is the range of black and white in a picture (or light and dark if you prefer). It should be used to help highlight the part of the image that you want the viewer to focus on. In my earlier piece my tones were pretty much in the same range, which means it's hard to visually distinguish the different planes in the piece (The ninjas, the castle, and finally the sky). In this grayscale version it's easy to see that the focus of the image is the ninjas. This was a conscious choice based on the fact that once this is shrunk down into a trading card, it would be hard to see any details on the castle anyway, so I might as well shift the focus to the parts of the piece that the viewer can see more clearly.
Since I was going to make such changes anyway, I decided to fix up some compositional issues I had with the earlier piece as well. I flipped the ninja on the right so that he's now facing the ninja on the left. This makes it look more like they're having a conversation, and also keeps the viewer's eye from moving out of the image. I also lowered the castle so that it wasn't distractingly close to the edge of the image, and now it neatly forms a triangle composition with the ninjas.
Now comes the hard part, color. In this image, I mostly maintain the tones that are set by the grayscale image. It looks okay, but seems a little dull to me.
This other color treatment feels more striking, and the castle and the ninjas both pop out. But I've basically screwed up the tones that I was working so hard to fix in the grayscale image, so I don't know if this is a good idea.
I'm gonna put this out for critiques again and will get back to you guys next week on what I ultimately decide to do.