One of the best I ever saw from an originality standpoint was someone was dressed with a white sheet over them with big blue stains, and tampons glued to the center of each stain. He was Picasso's Blue Period.
ok, bret the hitman hart is out. turns out we're doing a Nintendo Themed shit. I might say fuck it and just be a pirate. Might be TOAD. I was trying to pull off Eggplant Wizard but that'll be too hard. TOAD will look kind of lame though. Was also considering M. Bison from street fighter but the costume is like 60 bucks.
Get a giant cardboard box and paint it to look like the controller. See how many people come up to you and try to enter in the Contra cheat code.
Then buy a cheap suit and paint the buttons on. Make sure the "start" button is exactly where you want it.