Melt butter in a large saucepan over low heat.

Add marshmallows and stir continuously until completely melted and smooth.

Remove saucepan from heat and stir in green gel food coloring until the mixture reaches a uniform neon green shade.

Add puffed rice cereal to the green marshmallow mixture and fold gently until every kernel is evenly coated.

Press the mixture into a greased 9x9 inch square baking pan using a buttered spatula, ensuring an even thickness.

Allow the mixture to cool and set at room temperature for at least 30 minutes.

Cut the set treats into 12 rectangular bars using a sharp knife.

Melt black candy melts in 30-second intervals in the microwave until smooth.

Dip the top quarter of each bar into the melted black candy to create the hair and place on parchment paper to set.

Use a small drop of melted candy to adhere two candy eyes to the face of each treat.

Insert half of a mini pretzel stick into each side of the bar near the bottom to represent neck bolts.

Apply black decorating gel to draw a mouth and a small stitch scar on each face.