Line an 8×8-inch baking pan with parchment paper and lightly mist with nonstick cooking spray. Set aside. In a large pot over medium heat, melt the butter. Once melted, continue stirring as the butter begins to foam. The butter will foam up twice, and after the second time it will begin to turn golden brown and give off a nutty aroma. Immediately remove from the heat to prevent burning.
Carefully add the vanilla extract to the brown butter. The mixture will bubble and sizzle, so continue stirring for about 30 seconds until the bubbling subsides. Add half of the mini marshmallows to the pot and stir until almost completely melted. Add the remaining marshmallows and continue stirring until the mixture is smooth and fully combined. If needed, return the pot to low heat briefly to help the marshmallows melt.
Add the Rice Krispies cereal about 2 cups at a time, gently stirring until evenly coated in the marshmallow mixture. Fold in the roughly chopped mini pretzels and Oreos until evenly distributed.
Transfer the mixture to the prepared 8×8-inch pan. Lightly wet your hands or spatula with water and gently spread the mixture toward the edges of the pan. Be careful not to press down too firmly, as this can make the treats dense.
While the mixture is still sticky, evenly sprinkle the finely crushed Halloween Oreos over the top to create the dirt. Gently press the crumbs into the marshmallow mixture. Arrange the candy corn pumpkins across the top, lightly pressing each one into the Oreo dirt so it stays in place. Allow the treats to set at room temperature for approximately 15-20 minutes before lifting them out of the pan and cutting into squares. Enjoy!