Heat oven to 350°F. Place paper baking cup in each of 16 regular-size muffin cups; spray paper cups with baking spray with flour. Make brownie batter as directed; stir in dark chocolate chips. Divide batter evenly among muffin cups.
In small resealable freezer plastic bag, place vanilla chips; seal bag. Microwave on High about 20 seconds or until softened. Gently squeeze bag until chips are smooth. If necessary, continue to microwave at 10-second intervals. Cut off tiny corner of bag. Squeeze bag on top of unbaked cupcakes to draw ghost shapes.
Bake 24 to 26 minutes or until tops appear cracked and dry. Cool in pan 10 minutes. Remove from pan to cooling rack. Cool completely, about 30 minutes.