Preheat the oven to 350°F (175°C). Bake the brownies according to the package instructions and let them cool completely on a wire rack before cutting into ¾-inch cubes. Use about half of the cubes for the cheesecake.

Combine crushed Nilla Wafers, powdered sugar, and cocoa powder in a bowl. Stir in melted butter until it resembles wet sand. Press the mixture firmly into the bottom of a 9-inch springform pan. Bake for 8 minutes until set, then cool.

Beat room-temperature cream cheese and sugar until smooth and fluffy. Add eggs one at a time, mixing after each addition, then stir in vanilla. Gently fold in half of the brownie cubes.

Pour the batter over the cooled crust and tap the pan to release air bubbles. Drizzle hot fudge sauce on top in a spiral or zigzag and swirl it through the batter with a butter knife for a marbled effect.

Bake for 50–55 minutes until the center is set but still slightly jiggly. Turn off the oven, crack the door open, and let the cheesecake cool inside for 1 hour.

Cool completely at room temperature, then cover and refrigerate for at least 4 hours or overnight.

Remove the springform rim and slice with a sharp knife dipped in hot water and wiped clean between cuts. Top with extra hot fudge, whipped cream, cherries, or more brownie cubes before serving.