Place the heavy whipping cream, powdered sugar, and vanilla in a large bowl. Using an electric mixer, whip until soft peaks form (the consistency should be similar to Cool Whip).
Add the sour cream and gently fold it into the whipped cream.
Add the pineapple, mandarin oranges, maraschino cherries, grapes, coconut, and marshmallows; gently stir until well-combined (be careful not to break up the fruit or deflate the whipped cream).
Cover and refrigerate for at least an hour or two before serving to chill and to allow the flavors to blend and the marshmallows to soften a bit.