Prepare the Pan Preheat oven to 325°F (160°C). Line a 9x13-inch baking dish with parchment paper, leaving overhang for easy lifting.
Make the Crust Mix graham cracker crumbs, sugar, and melted butter until combined. Press firmly into the bottom of the pan to form a crust. Bake for 10 minutes, then set aside.
Make the Cheesecake Batter In a large bowl, beat cream cheese until smooth. Add sugar and mix until creamy. Beat in eggs one at a time, then add vanilla and sour cream. Reserve 1 cup of this batter for the pumpkin layer.
Make the Pumpkin Layer To the reserved 1 cup batter, add pumpkin puree, spices, and flour. Mix until fully incorporated.
Assemble Pour plain cheesecake batter over the crust. Spoon pumpkin batter on top and gently swirl with a knife.
Bake Bake for 40–45 minutes until center is just set. Turn off oven, crack the door, and let bars cool inside for 30 minutes. Remove and let cool to room temperature, then refrigerate at least 3 hours.
Decorate Sprinkle crushed Oreos over the top to resemble dirt. Place candy pumpkins on top. Pipe green frosting vines and leaves to complete the pumpkin patch look.
Slice and Serve Lift bars out using parchment overhang. Cut into 16 squares and serve chilled.