In a large microwave-safe bowl, combine marshmallows and butter and heat in the microwave for 1 to 2 minutes or until puffy. Stir until blended.
Add the Rice Krispies cereal to the marshmallow mixture and using a wooden spoon, stir until cereal is evenly coated.
Transfer into a lightly greased 9 x 13 baking pan and press firmly. Let the Rice Krispies cool for 1 or 2 hours.
Using a circle cookie cutter, cut out Rice Krispies into circle shapes and place in single layer on parchment-lined baking sheet.
In a microwave-safe bowl, heat candy melts in the microwave on 50% power for about 2 to 3 minutes, stirring every 30 seconds until melted.
Scoop melted chocolate into a decorating bag and cut a small tip off the end of the bag.
Unwrap peanut butter cup and apply a small amount of the chocolate on the top of the cup. Stick onto the center of each Rice Krispies treat, carefully pressing to secure.
Using the decorating bag, draw legs starting from Reese’s cup and onto the Rice Krispie treat.
Apply a small amount of melted chocolate onto the back of two candy eyes and attach to the top edge of the peanut butter chocolate cup, carefully pressing to adhere.