My daughter wanted to be a bat and wanted the wings to move. So I came up with the idea of using a black umbrella for the wings.
I just dressed her in a black dress, black tights, black boots. I purchased the black umbrella from the dollar store and then I cut it in half. I hot glued some black feather trim around the umbrella for extra effect. I allowed the silver joints of the umbrella to show b/c it looked like the little bones from a real bat. I sewed the umbrella along the underside of the arms and down the side of the dress.
I painted a black mask onto her face. Hot glued some "ears" on a headband that I made out of foam and painted black. Purchased a pair of inexpensive vampire teeth.