Awesome drawings. ^^ You've definately got the copying from a source down. The proportions are very well matched. Not a bad selection too.
All in all, very good renditions of the characters. Now step up your game and try your hand at charicatures or better yet, realistic renditions of cartoon characters. Or go the realistic route and try full body shots or multiple characters juxtaposed in new ways. I'd like to see that. ^^