Do the same as for Super Mario except use green stuff.
Thanks to Nick in Canada for another clever idea!!!
Another idea
Men's Costume
First, get a white sweater and green overalls. Also, wear some black shoes and a green hat (take a "NYC Taxi Hat" and dye green). Then paint a white circle on front, then put a green M.
Wear a black fake mustache, and dye hair black (if not already). Mama mia, you're Luigi! Luigi is copyright Nintendo
Thanks to GlitchKnight for this addition.
Another Idea
Hi, I'm Justin from Canada telling you how to be the lankier Mario bro, Luigi!
Put on blue overalls, and a green long sleeve shirt underneath. Put a green hat with a white semi-circle with a green "L" in the middle. Wear puffy white gloves and a fake moustache.
All you need is a slighty shorter friend to dress as Mario, and a girl to dress as Peach.
Thanks to Justin for this addition!