This year's costume reused (with several modifications) the backpack from my steampunk Frankenstein Monster costume. I took a month off from work to build the ray gun, and enlisted my friend to do some circuit building and arduino programming. The backpack smoked, there was a nixie tube countdown, a custom mixed audio track, the gears turned, the green on the side of the gun is a plasma disk, and it shot a rotating laserbeam. The barrel was supposed to Gatling around some green cathodes, but something went wrong with the 800+ volts that went to them. I hope to post a video of the thing in action one day. Oh, and I grew the facial hair for the costume.