Prepare and bake cake batter according to package directions, using 24 paper-lined muffin cups. Cool for 5 minutes before removing from pans to wire racks to cool completely.
For filling, in a small bowl, combine water and salt until salt is dissolved. Cool. In a small bowl, beat the marshmallow creme, shortening, confectioners' sugar and vanilla until light and fluffy; beat in the salt mixture.
Cut a small hole in the corner of a pastry bag; insert round pastry tip. Fill the bag with cream filling. Push tip through the top of each cupcake to fill center.
Place chocolate chips in a small bowl. In a small saucepan, bring cream just to a boil. Pour over chocolate; whisk until smooth. Cool, stirring occasionally, to room temperature or until ganache reaches a dipping consistency.
Dip cupcake tops in ganache; chill for 20 minutes or until set. Store in the refrigerator.