The last thing you’ll need is a set of bloody clothes that are also ripped here and there, and if you happen to have a lot of chest hair, joker costume get yourself a dress shirt that isn’t buttoned all the way up. You’ll then need a pair of monster fangs (even vampire fangs will do since no one could mistake you for a bearded Dracula), and you can even let your nails grow out a bit, and file them down until they are pointy, and then paint them down with some transparent nail polish to make them a bit more rigid.