In a large microwave-safe bowl, melt the butter and marshmallows together in the microwave, stirring every 30 seconds until completely melted.

Add the Rice Krispies to the melted mixture and stir until well combined.

Grease a baking sheet with butter or non-stick spray and press the Rice Krispie mixture into the pan evenly. Let it cool.

Melt the white chocolate melts in a microwave-safe bowl and stir in green food coloring until you achieve your desired color.

Dip the top of the cooled Rice Krispie treats into the green chocolate and add edible eyes while the chocolate is still wet.

Melt the milk chocolate melts in a separate bowl and dip the bottom edges of the treats, then sprinkle with black or brown sprinkles for hair.

Use remaining melted chocolate to decorate the mouth and eyebrows on the treats to create Frankenstein faces.