Decorate cake. Once buttercream transfer is chilled but flexible, remove from freezer and carefully wrap around cake, leaving parchment paper in place. Gently smooth with hand, using light pressure to make sure transfer adheres to cake. Chill cake until transfer is set, about 10 minutes. Carefully peel off parchment paper.
Fill decorating bag with ganache and snip end of tip off. Pipe drips of ganache down one side of the cake, dotting with ghost sprinkles at the end of each drip.
Place border of bat sprinkles around bottom of cake. Place meringues above ganache drips.
Using Gold Color Mist, spray candy topper gold. Let dry, about 10 minutes. Position on top of cake. If desired, attach trimmed-down lollipop stick with melted candy to back of topper and let set 5-10 minutes, then place.