This is just so utterly cute and it might as well be my first critique!

I really have to say that I love the colors you have used here , the light blues and complimenting hues really make these characters all the more visually appealing. It's really cute that Gumball is on Mordecai's back and I really like how you drew all of these characters in your own style!

The backgrounds seem a little too simple though, and there's a blank space that doesn't offer too much to the overall composition. The title is a nice twist on off of the shows, but I think it could have been executed a little better.

It's still a really nicely done picture and I'd love to see this same style on more cartoon characters!