Preheat the oven to 350 F. Line a 12 cup muffin pan with paper liners. In a large bowl, whisk together flour, sugar, cocoa powder, salt, and baking soda. Add in the eggs, melted butter, and vanilla extract and whisk until smooth.
Evenly divide the brownie batter between the paper liners. Bake for 15-20 minutes. Let cool completely. Spread frosting onto each cup and top with crushed Oreo cookies and a candy pumpkin.