1Heat oven to 350°F. Place paper baking cup in each of 24 regular-size muffin cups. In medium bowl, beat cake mix, buttermilk, oil and eggs with electric mixer on low speed 30 seconds. Beat on medium speed 2 minutes. Stir in 1 cup chocolate chips. Divide batter evenly among muffin cups.
2Bake 18 to 20 minutes or until toothpick inserted in center comes out clean. Cool 10 minutes; remove cupcakes from pans to cooling racks. Cool completely.
3In large microwavable bowl, microwave candy melts as directed on package. Place 1 marshmallow on top of each cupcake. Spoon melted candy over marshmallow to cover, letting excess drip down onto cupcake. Cool slightly. Press in 2 chocolate chips near top of each ghost for eyes. Let stand until set, about 15 minutes.