I seem to remember seeing a post about last-minute Halloween costumes on Buzzfeed last week, there may be some ideas there. Alternatively, you can make a passable ninja costume out of a couple of dark t-shirts (also required: dark trousers and shoes, obvs.) you should be able to find instructions for that by googling it. Failing that, a set of fangs should be easy enough to obtain. Throw in some artfully applied make-up and you've got yourself a vampire costume without having to go and get specific clothing.
Finally, you could just wear normal clothes and say you're a serial killer, a la Wednesday from the Addams Family movie.