Place the 9-inch chocolate pie crust on a flat surface or serving plate and set aside.
In a medium mixing bowl, beat 8 ounces softened cream cheese, 1 cup powdered sugar, and 7 ounces marshmallow fluff together until smooth, light, and free of lumps.
Spread the cream cheese mixture evenly into the bottom of the prepared pie crust.
Break the 6 Hershey’s chocolate bars into pieces. Reserve a few pieces for decorating, then place the remaining pieces in a microwave-safe bowl.
Microwave the chocolate pieces in the microwave-safe bowl in 30-second increments, stirring between each interval, until the chocolate is fully melted and smooth. Let the melted chocolate cool briefly until warm but not hot.
Divide the 16 ounces of Cool Whip into two equal portions (8 ounces each). Fold one 8-ounce portion of Cool Whip gently into the melted chocolate until evenly combined.
Spread the chocolate–Cool Whip mixture over the cream cheese layer in the pie crust, smoothing the top.
Refrigerate the pie for 3 to 4 hours, or until set.
Before serving, top the pie with the remaining 8 ounces of Cool Whip as dollops or piped swirls, sprinkle the reserved Hershey’s bar pieces over the top, and drizzle with hot fudge sauce as desired.