Add the cream cheese and 1/2 cup Splenda to a mixing bowl. Beat until it is smooth.
Add the sour cream and vanilla extract and beat until smooth.
Fold in the Cool Whip, then put 1/2 of the mixture in a separate mixing bowl.
To one bowl, add the unsweetened cocoa powder and tablespoon Splenda. Stir to combine.
In a small bowl add the PB2 powder and 3 tablespoons water. You want it to be creamy, but not watery. You might have to add an additional tablespoon of water.
Add the PB2 to the second bowl of cheesecake. Stir to combine.
Add the chocolate cheesecake to the bottom of a pie pan and spread evenly. Then add the peanut butter cheesecake and spread evenly.
Cover and refrigerate overnight.