Melt the butter in a large saucepan over low heat.
Add the mini marshmallows and stir continuously until completely melted and smooth.
Remove from heat and quickly stir in the Rice Krispies cereal until fully coated.
Add green food coloring and mix well until the color is evenly distributed.
Press the mixture into a greased or parchment-lined 9x13-inch baking pan. Let it cool slightly.
While still warm but set, cut the slab into 12 rectangular bars.
In a microwave-safe bowl, melt the chocolate chips in 20-second intervals, stirring in between until smooth.
Use a spoon or piping bag to add chocolate “hair” to one end of each rectangle.
Place two candy eyes below the chocolate hair on each bar.
Insert two pretzel stick halves on each side of the base for bolts.
Use more melted chocolate or decorating gel to add a mouth.
Let the treats cool completely before serving so the decorations stay in place.