Butter a 9″ x 13″ casserole dish and set aside.

In a large pot over low-medium heat, melt the butter.

Add the mini marshmallows to the pot and stir continuously until smooth and fully melted.

Stir in the Rice Krispie cereal with a spatula until evenly coated.

Transfer the mixture to the prepared casserole dish and press it down evenly until the top is flat.

Allow the treats to set for about 30 minutes.

Once cooled, remove the Rice Krispie slab from the dish and cut it into rectangles of various sizes.

Melt the green candy melts using a double boiler (place a bowl over a small pot of boiling water). Stir until smooth. If too thick, add a teaspoon of vegetable shortening.

Dip the tops of each treat into the melted green candy, then immediately into the black jimmies to create “hair.”

Press two royal icing eyes onto each treat below the sprinkle hair.

In a small microwave-safe bowl, melt the black candy melts in 10–15 second increments, stirring in between.

Transfer the melted black candy to a piping bag and pipe “stitches” onto the treats to complete the Frankenstein face.

Let the treats set completely before serving or packaging.