In a large, microwave-safe bowl, add peanut butter, butter and 1/2 cup of chocolate chips. Microwave in 30 second intervals, stirring after each, until mixture is smooth. 

Add in the marshmallows and microwave for 1 minutes. Stir until thoroughly combined. 

Pour the cereal over and use a spatula to fold together until the cereal is evenly covered with marshmallow mixture. Set aside to cool slightly. 

In a small microwave safe bowl, melt the remaining 1 cup chocolate chips in 30 second intervals, stirring after each, until smooth.

Spray hands with cooking spray. Pull off a lime-sized amount of cereal mixture and shape into a flattened oval. Repeat with remaining cereal. 

Stick 6-8 pretzel sticks into sides of oval for spider legs. Use cookie frosting to attach eyes to front of body. 

Lay out prepared spider bodies on cookie sheets lined with wax or parchment paper. Snip off the corner of your chocolate bag (if using) and pipe a line of chocolate along the top of the pretzel sticks. Place in refrigerator to set for 10-15 minutes.