Step 1: Preheat oven to 350°F (175°C). Grease a 9-inch springform pan and line the bottom with parchment paper.
Step 2: Prepare brownie batter by mixing brownie mix, 1 egg, vegetable oil, and water in a bowl until smooth. Spread evenly in the prepared pan.
Step 3: Bake brownie layer for 20 minutes until set but not fully cooked. Remove from oven and let cool slightly.
Step 4: In a separate bowl, beat cream cheese, sugar, vanilla, and remaining 2 eggs until smooth and creamy.
Step 5: Spread half of the cheesecake mixture over the warm brownie layer. Drizzle with 1/2 cup hot fudge sauce.
Step 6: Top with remaining cheesecake mixture, spreading evenly. Return to oven and bake for 35-40 minutes until center is set.
Step 7: Cool cheesecake completely at room temperature, then refrigerate for at least 4 hours or overnight.
Step 8: Before serving, warm remaining 1/2 cup hot fudge sauce. Top cheesecake with whipped cream, cherries, peanuts, and sprinkles. Drizzle with warm fudge sauce.