Preheat oven according to the brownie mix package instructions. Prepare the brownie batter as directed.
Bake in a greased 9×13-inch pan until set, then let cool completely.
Cut brownies into squares or circles using a sharp knife or cookie cutter.
Carefully break each cookie half into two equal pieces to form bat wings.
Press two cookie wings into the sides of each brownie piece.
Use a dab of melted chocolate or frosting to attach two candy eyes on top.
Chill brownies for 10 minutes to help the decorations set, then serve.
