For the cookies use the recipe you prefer. I used this car cutter, and a round one for the moon. Bake them and cool.
I prepare two different gray icing, light and dark, a green and a yellow one. I left also some white.
First I outlined the cookies like in the photo.
I flood the whole cookies with the light grey icing. Immediateli on the right side I put over the darker grey, just to have a shade effect. I mixed them with a toothpick. I leave them dry for 30 minutes, not at all. With a darker grey I made the round dots for moon craters. At the right side of each crater I put some white color.
BAD PIGGIES UFO
I flooded all light grey parts. Then I draw the piggies head. Fill the white. I let them dry.
Then draw all details on the piggies head, outline once again the ufo and put the details. With the yellow draw the fire, the lights and the lines.