This was the best costume that we have ever made. My daughter is 8 years old and she was a big helper. We went to our local thrift store and bought a couple of trench coats. They were on $2.00 each. I wasn't sure what size we would need. My daughter is small but it ended up that we needed a large adult coat. We didn't use the buttons because I thought if she tripped or fell it would be to hard to rip open. Instead we closed the coat using velcro.
Step 1: Plastic container
We tried different size containers. The one that was big enough was a pretzel container that we got from our local grocery store. We cut the entire bottom out of it. We cut half of the back out too. We put black duct tape around all the edges so they would not scratch her. We took the lid off and rubberband a piece of thin material around the top. Once she wore the costume for awhile the inside would start fogging up so we decided to remove the cloth from the top and kept it open . Our daughter said it was better that way. More air flowed through. We added cotton balls to the bottom and dripped fake blood around the bottom.