Preheat the oven to the temperature called for on the brownie mix box. Prepare an 8x8 baking dish by greasing with butter or oil. Set aside.
In a mixing bowl, prepare the brownie mix by following the directions on the box.
In a smaller bowl, mix together the sugar, pumpkin puree, butter, and egg until smooth. Stir in the flour, salt, baking soda, and cinnamon until everything is just combined.
In the prepared baking dish, add 3/4 of the brownie batter and spread evenly. Add 3/4 of the pumpkin batter to the top of the brownie mix and spread gently.
Using the remaining brownie and pumpkin batters, sporadically add dollops across the surface. Gently swirl the two batters together using a butter knife or offset spatula (don't mix too much; just a little bit of swirling gives the best look).
Bake according to the directions on the brownie mix box. Allow to cool before slicing.