Line a small baking sheet or baking dish with wax paper and set aside.
In a pan large enough to hold all the ingredients, melt butter over medium low heat, then add marshmallows. Stir constantly with a wooden spoon until marshmallows are completely melted and incorporated with the butter. Remove from heat and add peanut butter and vanilla extract, mixing until well combined.
Add rice krispies cereal and mix well. Pour mixture onto baking sheet, pressing down into a single layer. Note: Spraying your hands with a little cooking spray helps keep mixture from sticking to your hands. Let cool completely, about 1 hour.
Decorating
Using a cookie cutter, cut out your ghosts from the rice krispies treats. You can put the scrap pieces into the microwave for 30 seconds at a time to soften them up to reshape if desired. Depending on your spacing, you should get about 16 ghosts per batch of rice krispies treats.
Melt bark per package instructions. Using a fork or chocolate dipping tools, dip treats in the chocolate until well coated. Gently shake any excess chocolate off and place on baking sheet lined with wax paper. Repeat until all treats are covered. Chill in refrigerator for 30 minutes.
Melt peanut butter chips in microwave for 30-60 seconds. Once completely melted, put in a piping bag equipped with a very small decorating tip (around size 6). Pipe out eyes, mouth, and outline ghost edges. Let the peanut butter chips set and enjoy!