One of my favorite props, the Ulaks from The Chronicles of Riddick Movie and The Assault on Dark Athena video game were fairly easy to build. The X-ACTO Ergo and a fantasy knife called the Swing Blade are the two main components in the build. The handle of the Ergo knife was heavily modified on the inside to fit around the handle of the Swing Blade knife. Once bolted together the seams were filled with bondo and painted. The knife was detailed with multiple layers of flat black paint, coated in Plasti-Dip for a rubberized texture and finally weathered with pastel chalk. The blade itself was weathered with acrylic "mud and blood," and rough spots were created with steel wool to facilitate the growth of a bit of rust.
The knife was very sharp so it needed some sort of display. In the movie, the knife was used on the volcano planet Crematoria, so I designed the display to emulate the surface of the planet. Pillows of hardened lava were created with expanding foam on a steel backing. I added an image from the DVD cover as a name plate and attached the knife to the steel backing with magnets.