Line a 9x13 casserole dish with parchment paper.
Layer graham crackers evenly into bottom of dish. About 8 crackers, some may need to be broken up to fit and lay properly.
In a large bowl, add defrosted cool whip and marshmallow fluff and whisk together until as smooth as possible. Spread over graham crackers.
Sprinkle chopped Reese's on top of cool whip mixture.
Prepare pudding by mixing together pudding mix with cold milk. Once set, pour over top of cool whip and Reese's layer and spread evenly.
Drizzle peanut butter on top of pudding mixture, then top with 8 more graham crackers, again fitting crackers as evenly on top as possible, breaking some into pieces if necessary.
Freeze for at least 4 hours. Cut into and serve! If frozen for longer (overnight), let sit at room temp at least 10 minutes before eating.