I love the colors and the yellow-bluish/green gradient that absorbs the viewer into this gentle world. Characters and the colors are both resonating in the same peaceful vibe. Even though there is a beast in the picture, its expression is so calm and nonthreatening, it goes perfectly with the rest.
I see that you chose to draw this in a drawing manner, where instead a precise one line "made with ruler", a view can see the lines as drawn with pencil, multiple times for one line. And this is where I would make the only change in this picture, I would use this style for stares, tower and the boy, but as the view goes up, the beast would be drawn more precisely, more realistically, without this cute drawing-style clumsiness, with more details.
This is it. I like it a lot, and I made one remark that in my imagination would made it half grade up. Good luck.