Place the cream cheese, two tablespoons of the sweetener, and the cocoa powder in a blender. Pour the warm water and peppermint extract over top and blend until smooth and creamy.
In a large bowl, beat the whipping cream with the remaining sweetener and the vanilla extract until it holds stiff peaks. Remove a few tablespoons of the whipped cream for decorating.
Fold the chocolate mixture into the remaining whipped cream until no streaks remain. Spoon the mousse into 4 dessert cups and refrigerate at least 30 minutes to firm up.
Top with a dollop of the extra whipped cream before serving.