In a microwave safe bowl, melt 3 bars of dark chocolate using 10 second increments and stirring between each heating. Line an 8" x 8" baking dish with plastic wrap, and spread your melted dark chocolate evening over the surface. If you'd like to add any candy or cookie pieces to give your candy bark a little something extra, now would be the time to do that. Refrigerate the dark chocolate until hard.
In another microwave safe bowl, heat 2 bars of white chocolate, and spread it over your first layer of chocolate. Refrigerate again until the white chocolate has hardened.
Melt the final 3 bars of dark chocolate and 1 bar of white chocolate in two separate bowls. Spoon a little bit of the dark chocolate into a piping bag, and spread the rest over the hardened candy bark. Spoon all of the white chocolate into a piping bag. While the final layer of chocolate is still warm, start creating ghosts by piping circles of white chocolate. Using a pointy object like a toothpick or a meat thermometer, draw one end of each circle out to create a tail. Using the dark chocolate in the piping bag, add eyes and mouths. Add some festive sprinkles or leave the top as it is!