This is probably one of my most favorite "DIY" projects that I executed this year!
I took the print out off of Google Image Search... and added my own interpretation.
I used this template for the shape of the bats. I folded one black sheet of paper in half (the Hot dog way) and then put the middle of the bat toward the crease. that way, when I cut it out, it gave me one full bat with a crease down the middle when I was done.
I cut out 45 Bats total for my look, but you could do more/less depending on what size of wall you're covering, or what you want to do with them. I kept growing my swarm because I had them left, and I didn't want to throw any away, or move them to a different wall, but I really like the way it turned out.
The Instructions are to make a "Mobile" or to "Hang" the bats... but I just really liked the shape of these ones, so I cut out several of each size, and used a little "Quake Hold" or poster putty to affix the bats to the wall in a 3D type manor.