The sword was purchased at the dollar store for (you guessed it!) $1. and we wrapped some red and black ribbons around the handle and attached them with hot glue, ( a busy moms best friend!). You can create a basic black robe without any sewing, instructions here.
Generally speaking, we always keep several black robes in various sizes in our Halloween Trunk for putting together last minute costumes. Each year it seems the kids are invited to several different parties and goddess forbid they wear the SAME costume to each party.
If you're really in a hurry, you can simply use black pants, black shirt, black shoes and a black sash to wear as a belt. If your child only has white shoes, consider slipping on a pair of black socks OVER the white shoes (once they are on your childs' feet!).