Grease a 9×13-inch baking pan with nonstick cooking spray. Set aside.

In a large pot, melt butter on low heat. You’ll want to keep the heat low so that the butter melts but doesn’t brown.

Once butter has melted, add the mini marshmallows.

Once marshmallows begin to melt, stir in the peanut butter. You'll need to stir the mixture constantly until the marshmallows have completely melted and everything is combined.

Remove from heat.

Stir in the Rice Krispies.

Pour the cereal mixture into the prepared pan, and gently press it to form an even layer.

To make the topping, add the chocolate chips to a microwave-safe dish.

Microwave for 30 seconds. Stir.

Add the coconut oil, and continue microwaving and stirring in 15 second intervals until melted and combined.

Pour the chocolate mixture over the bars, and spread to combine.

Let set up for 30 minutes, or until set, before cutting and decorating.

Remove from pan and cut treats into squares. Set aside.

To make the spiders, microwave the candy melts at 50% power for 30 seconds. Stir. Continue microwaving and stirring in 30 second intervals until smooth and melted.

Add the melted candy mixture to a piping bag with a small tip.

Add a peanut butter cup in the center of each cut square.

Using the piping bag to add legs starting from the peanut butter cup and moving outward.

Add two small dots of melted chocolate to the front of the peanut butter cup and then gently press the candy eyes to the peanut butter cup.

Let the decoration set up and cool before serving.