Prepare cake according to package directions.
When cake is finished baking, immediately poke holes all over the top using the back of a wooden spoon.
Add peanut butter to a microwave safe bowl and microwave on high for 45 seconds, or until peanut butter is thin.
Stir in 1/2 cup of candy pieces.
Pour peanut butter mixture over top of the cake, using a spatula to spread it evenly.
Allow to cool.
In a large bowl, mix whipped topping and chocolate syrup; spread on top of cooled cake.
Top with remaining candy pieces.