Melt the butter in a large saucepan over low heat. Add the mini marshmallows and stir until fully melted and smooth.
Stir in the cocoa powder until it is evenly mixed into the marshmallow base.
Add the green food coloring a drop at a time, stirring until the mixture reaches a consistent green shade.
Remove the pan from heat and quickly fold in the Rice Krispies cereal until every piece is coated.
Press the mixture into a greased 8x8 pan or shape it by hand into four rectangular bars while it is still warm.
While the bars are still soft, press two candy eyes onto each one and insert two pretzel sticks on the sides to look like bolts.
Let the treats cool at room temperature for 20 minutes before serving.