Multiple bright lights are mounted to the ceilings and walls of the room to cast distinct shadows. The lights should also be able to swivel to creating moving shadows in the harder rounds of the game.
Infrared distance sensors can be placed at about each four inches along each of the four walls of the room to determine where each player is standing and whether or not they're standing in a shadow. It is useful to have sensors along each wall so that it can accomodate for the situation in which players are all standing in line with a sensor. In this case, only having sensors along some of the walls may mean that a portion of the players are "hidden" to the sensors.
The dark figure can be a simple hooded figure. The figure should also be easy to make since there will be multiple figures in the room. Ideally the figure a bit creepy, but not too scary. It should also be strong and difficult to break.