Things You'll Need
Instructions
Make a Darth Nihilus Costume
Take a look at an image of the Darth Nihilus costume. If you don't have a drawing or image of the mask there are several online (http://starwars.wikia.com/wiki/Darth_Nihilus). Get a sense for the overall aesthetic of the character before making anything.
Obtain a long, dark cloak with a large hood. All Sith lords wear a very large cloak that is absolutely jet black. You will also need black gloves, boots, socks, pants, and a long sleeved shirt. No part of your skin should be showing in the Darth Nihilus costume.
Draw or trace the Darth Nihilus mask onto a piece of sturdy cardboard. The Nihilus mask is shaped like a human skull, but with very large, ovular eye sockets. The entire nose area is open with a dark line running up the center of the face. Above each eye there is a thick red line running up into the skull.
Cut out the holes in the skull for the nose and eyes. Paint the mask a dull white or silver color. Staple a band of black elastic to both sides of the mask so that it can be attached to the wearer's head.
Attach the top of the cloak to the top of the mask with strong fabric glue. I recommend also creating a rectangular wire support to hold the hood out from the head. Simply bend a piece of thick wire into a rectangle and place it snugly on top of your head before putting on the hood.