
There are some pretty neat WCC projects floating around out there but all of them sort of forgot that our friendly cube is weighted, not a stuffed and cuddly plush toy or a flimsy papercraft. I decided if I wanted to do it right, I would need to make him myself. And now you can too!
This was a pretty rushed project, so let's hope yours turns out better than mine. :)
Materials:
Sculpey
Armature Wire
Acrylic Paints
Sand Paper and/or Steel Wool
Sculpting Tools
Turpenoid (optional)

To start, I measured out a 2 inch cube using 16 gauge armature wire. I felt that since it was so small I didn't need to use any aluminum foil or epoxy cement. This, in retrospect, was really stupid. Do as a I say and not as I do: fashion your base out of both foil and wire, then make the corners sturdy with some cement. You want it strong.
I built up the Sculpey into sheets and lathered it on one side at a time, making sure it was packed in tightly so it wouldn't cave in. Each side probably measured about half an inch thick. My improvised armature came back to haunt me and the cube ended up being sort of uneven and lumpy. But there's no sense crying over every mistake; you just keep on trying till you run out of cake.
I could have measured the corners to perfection but that was far too much work for a lazy person like me. I threw on six circles and the little decals, evening everything out with a couple of tools. You don't really need any tools, but it will save you a lot of time and frustration. Ideally I would have picked up gray pins with hearts on them for a perfect metallic effect but it's not like I had six of them laying around for such an occasion.
When it looked done I carefully smoothed all the tiny cracks and inconsistencies with a paint brush dipped in turpenoid. Be sparse with this stuff - it could kill you and your companion cube.
You did it! The weighted companion cube certainly brought you good luck. However, it cannot accompany you for the rest of the test and must, unfortunately, be euthanized. Please escort your companion cube to the Aperture Science Emergency Intelligence Incinerator.
I used 250° and a longer baking time than the recommended 275° to prevent any cracking. The sculpture was probably an inch and a half at the corners so I kept it in the oven for two hours.
I sanded down the corners with sand paper and steel wool, starting with heavy duty stuff and finishing it off with fine grain. This gave a more smooth and even surface as well as brought out the "cube" that might have previously been a misshapen "lump."
Paint time. I had a limited amount of colors and got by on white, black and red until it came to the hot pink crevices on the sides. Bright neon colors cannot be mixed - the closest you'll get is a dull fuchsia by mixing violet and red so keep that in mind.
I used two coats and let it dry. My cube seemed a little bit lacking so I mixed a darker, diluted gray and graced it with more of a worn look, purposefully adding imperfections.
The weighted companion cube is now complete and ready for cake!
...My cat isn't really sure what to think about it.