In a medium bowl, mix graham cracker crumbs, granulated sugar, and melted butter until well combined. Press this mixture firmly into the bottom of a 9-inch springform pan, ensuring an even layer. Chill the crust in the refrigerator for about 30 minutes to set.

In a large mixing bowl, beat softened cream cheese and powdered sugar together until creamy and smooth, about 2-3 minutes. Add vanilla extract and marshmallow fluff, mixing until just integrated. Gently fold in the whipped cream using a spatula.

Pour the creamy filling over the chilled crust and spread evenly. Cover with plastic wrap and refrigerate for at least 4 hours, or overnight until firmly set.

Combine remaining marshmallow fluff and whipped cream to make the topping. Whip until light and fluffy, about 2-3 minutes, then spread evenly over the cheesecake.

Optionally, decorate with mini marshmallows or crushed graham crackers. Refrigerate for another hour before serving to meld flavors.