The green aliens are my favorite Toy Story characters so they had to be included in the party. I found this idea online through Disney. If you go to the link you will find detailed instructions on how they made theirs. Mine were similar with a few differences. I used fondant to make the eyes and poked black licorice into the balls for pupils. The aliens had two mouths, one being black fondant and the other being black licorice. The antennae were made from sour straw candy, cut into 2" pieces and topped with a green cake decoration (buttercream was the glue). The ears were made from rolls of sour green candy that I found at a gas station, of all places. (This was by far, the hardest ingredient to track down. I went to candy stores, pharmacies, etc. and almost jumped out of my skin when I found the strips at the gas station by accident.)
I assembled all of the pieces, a day in advance. The pieces were stored in plastic containers. The cupcakes were vanilla with vanilla buttercream. I frosted the cupcakes and then added the parts that had already been assembled.