I can't help, but make sure you get ninja slippers with separate toe holes (for climbing lamp posts I think?) Or poking someone in the eyes with your feet?
Don't turn up. Then the next day say that you were there all along. Everyone will think your costume was amazing. True story.
what about a little plastic ninja sword and a set of shiruken to finish off Makhaira, Regarding not turning up but saying you were there-how did you get away with that one?-knowing may come in handy some time!
Black t-shirt, so easy and looks authentic. sometimes I do it just at home in the house for fun and to get in touch with my ninja chi. http://www.wikihow.com/Make-a-Ninja-Mask