Preheat oven to 350 degrees F. In a small bowl, add in the Oreo baking crumbs (without the cream) and melted butter. Mix until the butter is evenly distributed. The Oreo crumbs should appear wet.
Place crust mixture into a 9x9 pan that is lined with parchment paper (ideally) or sprayed with non stick spray. Spread the mixture out evenly and press down with a spoon to compact the crust.
Bake for 8 minutes. Once finished, take out of the oven, and set aside leaving the oven set at 350 degrees.
Start the filling by placing the softened cream cheese and sugar into a mixing bowl. Beat until smooth and creamy. Add in the eggs and vanilla extract. Once well combined, add in the marshmallow fluff and mix.
At this point you can add in things like chopped up cookies, sprinkles, chocolate chips etc.... Use a spoon to gently fold in until well incorporated.
Pour over the crust and spread evenly. Bake for 20 minutes. Once the 20 minutes are up, without opening the oven door, reduce the heat to 200 degrees and bake for an additional 30 minutes.
Once finished baking, turn the oven off leaving the cheesecake inside for 10 minutes. Remove, set on a cooling rack and allow the cheesecake to come to room temperature.
Once at room temperature, cover, and place in the refrigerator for at least 3 hours. When chilled, take out and cut into 12 squares.