1. In a large bowl, combine the cake mix, water, butter, and eggs. Mix until combined. Next, cut up Butterfinger candies into chunks and mix into this batter.
2. Grease the slow cooker with cooking spray. Pour the cake batter into the slow cooker.
3. Cover the slow cooker and cook on high for 2 hours, or until a toothpick inserted into the center of the cake comes out clean.
4. Once the cake is done, turn off the slow cooker. Heat up the hot fudge and top the cake off.
6. Sprinkle additional crushed Butterfinger candy bars over the top of the cake.
7. Serve warm with a dollop of whipped cream on top.
