This artisitic thaught occured to me when the bin was stuck open and I was going to put an empty bottle near it.
Here's what you do,
Take something like paperclips or wire and make a frame skeliton of your Alien (they are the black acid guys, don't get confused like I did at first), then stick banana skins all over it and as their head is shaped like a banana use a whole banana there, put in the sun for two days to rot, and it will get a beutiful alien black texture.
Enjoy kids!