Grease a baking pan lightly with butter.
Melt butter in a large saucepan over low heat.
Add marshmallows and stir until completely melted.
Add green food coloring and mix well.
Remove from heat and stir in Rice Krispies.
Mix until cereal is fully coated in green marshmallow.
Press mixture into the greased baking pan evenly.
Allow mixture to cool for 30 minutes.
Cut cooled treats into neat rectangular bars.
Dip top edges in melted chocolate for hair.
Add candy eyes using chocolate as edible glue.
Draw mouth and stitches with black decorating gel.
Press small candies into sides as Frankenstein bolts.
Let chocolate details set before serving.