You could make a James Bond-styled movie about how Mario and Luigi break into Bowser's secret castle in the sky using awesome technology. Mario could be the complete scaredy-cat moron and Luigi could be the one that plans everything out.
I dunno.
Heh, I estimate I've made nearly 20 minutes of Mario-related animation in total. Video game parodies are very fun to make.
FadePuff
Would help to know which kind of movie you're making. However, Yoshi is a good side kick, comic relief, etc. kind of character that would be easy to fit in.
Nickclick2
Like, I meant minor characters, but Yoshi'll work.
I'll put you in the credits if I use him, along with the sprite creator. :)