I was strapped for time and money for a Halloween costume, so I decided to go old-school, and get creative with a pair of boxes, construction paper, and sharpie. If you are able, sewing the boxes together made the costume much more durable.

Step 1: Materials

What was used:

2x 2'x3'x2' boxes from UPS store. $10 each. Most expensive part.
1x 1'x2' piece of red construction paper. $1 from a craft store.
8x standard printer paper. Had some lying around
Glue.
Pencil. I drew most of this free-hand. You can use a measuring device if wanted.
Sharpie
Staples -or- Needle and thread. I needed some way of joining the 2 boxes.

Step 2: Start the Outline

First, close one end to one box. This will be the top of the costume. Using a picture of Domo, either from my costume or an internet search, sketch out approximately where you want the eyes and mouth. My eyes were about 3-4" diameter, and the mouth was 22" x 12". You will want to also trace out where you will cut holes for your head and arms later.

Step 3: Designing the Mouth, Eyes

Next I cut my piece of red construction paper to the outline on my box. Domo has 8 teeth total, 4 top and 4 bottom, so I took 8 sheets of printer paper and tried my best to make a 6" equilateral triangle. With one drawn out, I stapled all the papers together, and cut all the teeth at once. I then layed out all the teeth on the red paper, and glued all the teeth into place. After a couple minutes of drying I glued the mouth onto the spot I had reserved on the box for it.

For the eyes, fill in the circles with sharpie.

Step 4: Construct the Body

Once the glue is dried and you can stand the costume up without the mouth falling off, cut open the holes for your head and arms. Start by cutting small holes, because it is much easier and prettier to make them bigger than to try to make them smaller.

I attached the lower box to the head originally by stapling the box's flaps to one another, but my staples weren't long enough to go through 2 layers of cardboard. Instead, I decided to sew the pieces together. I also cut off the lower flaps of the lower box, to reinforce the shoulders of the costume.

Step 5: Sewing the Body

Sewing the body was the most time consuming parts. I poked 2 holes through each flap, one on top of another, so I could sew a few loops of string through. This kept the whole body straight, too. I also took leftover flaps, and sewed shoulder reinforcement onto the costume.