01 - Dissolve orange gelatin in 2 cups boiling water. Stir until completely dissolved, then stir in 1 cup cold water. Let mixture cool for 10 minutes.
02 - Gently fold drained mandarin oranges and crushed pineapple into cooled gelatin.
03 - Pour mixture into a 9x13-inch glass dish or decorative serving bowl. Refrigerate for at least 2 hours until completely set.
04 - In separate bowl, fold together sour cream, mini marshmallows, and whipped topping until well combined.
05 - Spread creamy mixture evenly over set gelatin. Refrigerate for at least 1 additional hour before serving. Garnish with extra mandarin oranges or orange zest if desired.