Transfer hot fudge ice cream topping to a small microwave-safe bowl.
Heat according to package instructions, or for about 60 seconds, until melted and thinned.
Carefully spread in an even layer on the bottom of the pie crust. Watch that pieces of the crust don't "lift" up as you spread.
Refrigerate for 15-20 minutes, or until hot fudge is set.
Meanwhile, prepare peanut butter pie filling.
In a large mixing bowl, beat 4 oz. cream cheese until smooth.
Add creamy peanut butter, 1 cup powdered sugar, vanilla extract, and 1 cup whipped topping, beating until smooth.
Fold in another 1 cup whipped topping.
Spread the peanut butter filling evenly over fudge layer in the pie crust.
In a small mixing bowl, beat remaining 4 oz. cream cheese until smooth.
Add marshmallow fluff and remaining 1/4 cup powdered sugar, mixing until smooth.
Fold in remaining 1 cup whipped topping.
Spread marshmallow fluff mixture over peanut butter layer in the pie crust.
Refrigerate for at least 2 hours, or until thoroughly chilled and firm.
If desired, top with graham cracker crumbs, chocolate chips, and mini marshmallows, for garnish. Cut and serve.
Store in refrigerator for about a week.