Step 1: Grease a 9×9 inch square baking pan with butter or line it with parchment paper for easy removal.
Step 2: In a large pot, melt the butter over low heat. Once melted, add the mini marshmallows and stir continuously until they are mostly melted.
Step 3: Remove the pot from the heat and stir in the vanilla extract and crispy rice cereal until the cereal is evenly coated with the marshmallow mixture.
Step 4: Press the mixture gently into the prepared pan using a buttered spatula. Let the treats cool completely at room temperature for about 30 minutes.
Step 5: Cut the cooled treats into 12 rectangular bars.
Step 6: Melt the candy melts in separate bowls in the microwave in 30-second increments, stirring until smooth. Add a tiny bit of coconut oil if the chocolate is too thick.
Step 7: Dip the top half of each treat into the melted candy and immediately press on candy eyes to create your monster faces. Let set until the chocolate is firm.