1. Add grape juice to a saucepan over medium heat. Let simmer until grape juice reduces and thickens to a glaze consistency (this will take some time, it depends on the size of your pot). Let cool, then refrigerate if you’d like it to thicken more (or leave at room temperature).
2. In the bowl of an electric mixer, whip whipped topping until stiff. Add cream cheese, peanut butter, and confectioners’ sugar. Mix until combined.
3. Add mousse to a piping bag and pipe into dessert dishes. Using a spoon, drizzle grape juice sauce on top.