It looks really cool. The flat sky needs more depth if you can. Maybe a gradient starting lighter at the bottom up to the color you have now at the top?
I really like the creativity and the colors. I agree that the sky needs more depth, but I still really like it! It's very fun
This piece is so cute, I do like that you have the pink and yellow bubbles coming out of the koala's jet pack.
The colors you added to this are pretty nice and the picture is very cute. It might be just me, but the gas/exhaust coming out of the koala's jet pack looks particularly toxic. Is this intentional?