No-sew costumes must have been invented with me in mind. Although I would love to be able to sew, I can't. And I don't have a sewing machine. So, if I can come up with a creative Halloween costume idea for one of my kids without having to thread a needle, color me a happy camper. For me, the perfect costume is one that is simple, uses supplies I might have already on hand or can pick up easily, and that my child will tolerate wearing for several hours at a time (your fancy box robots need not apply). Butterfly Catcher for my 2-and-a-half-year-old little munchkin? Let's go!
Cost: $3. I bought the tablecloth, the necklaces, and the butterfly net from the dollar store. Her shirt, the glitter, and paper plates we already had on hand.

Choose a color scheme first. This will help you decide which plastic tablecloth to purchase and what color glitter to use. I didn't want to go for the obvious choice of pink for my daughter (even though she loves the color), so I chose her second favorite, purple, accented by pops of green and orange.

For the skirt: Buy a plastic tablecloth. I purchased a solid purple one from the dollar store. The standard size should provide plenty of fabric. You can go with a solid color or one of the many floral varieties that are readily available. Just check the thinness of the tablecloth to make sure it's not see-thru. With the standard length, you can always double it to make certain it's not too thin.

Using my daughter's height as a guide, I cut the tablecloth in half horizontally. Once that was done, I folded it in half, and after measuring her waist, I cut a hole in the center so she could step into the skirt. Since this is No Sew (and we're working with a plastic tablecloth), I used a small binder clip and cinched the back of the waist (once the skirt was on) to make sure it was snug on her. Her coordinating shirt very easily covered the clip.

I arranged the skirt so that it was a little shorter in front, leaving a pretty trail behind my daughter as she walked. That way, it was a longer skirt, but didn't pose any tripping hazard.
For the butterfly decorations on the skirt: On your paper plates, using a permanent marker, draw the outline of a butterfly. I googled "butterfly template" and using that printout as a guideline, I drew a butterfly on each of the paper plates, using most of the available white space. The age and size of your child will determine how many butterflies you will need. I made seven butterflies to place in various spots around the skirt. Once you have your butterflies outlined, cut them out. Using glue, fill in the butterfly and apply glitter. I glittered the body of the butterfly in green and let it dry. Then I went back and, using a mix of purple and pink glitter (mixing the two colors to give the butterfly a little more depth), filled in the wings. Set aside the butterflies and let them dry overnight. Once dry, fold the wings back a bit, so when they are applied to the skirt they don't sit flat and adhere better. Using Velcro fasteners (because that will hold up for a few hours of trick-or-treating), apply the butterflies onto the skirt.
Putting it all together: I chose a shirt that my daughter already had to coordinate with the skirt. At the dollar store, we grabbed a handful of sparkly Mardi Gras necklaces for her to wear around her neck. A butterfly net completed the costume.