What Chu runnin to?

Very cute. I especially love the Pichu. <3

I will say that your lines are very messy. Using the pen-tool makes getting clear lines very easy and you can find plenty of tutorials on the pen-tool here on the site if you aren't familiar with it.

You should work more with values. Right now your highlights and lowlights blend in with your base colors, so they look very flat. Think of areas that are getting absolutely no light. Those should be your darkest areas. Don't be afraid to use darker shades for shadows.

The background could use a little bit of work. I understand why you used the blurry effect, but you don't have a clear foreground, so the blur effect which would be used to create distance is rendered useless.

Lastly, clouds can be quite difficult. I often use cloud brushes (by ~SilkAssassin) since I'm much too lazy to paint them myself, but something to keep in mind is that even clouds have shadows. Take a look at the sky next time there's a nice day with a blue sky and a couple clouds in the sky and really study what you see. <3

Hope I was of some help to you! <3