01 - Pour orange gelatin powder into a large mixing bowl. Add 2 cups boiling water and whisk continuously until crystals completely dissolve. Stir in 1 cup cold water and let mixture cool for 10 minutes.
02 - Gently fold drained mandarin oranges and crushed pineapple into cooled gelatin mixture, taking care not to break up fruit segments.
03 - Transfer mixture to a 9x13-inch glass dish or decorative serving bowl. Refrigerate for minimum 2 hours until completely set and firm to the touch.
04 - In a separate bowl, combine sour cream, mini marshmallows, and whipped topping. Fold together with spatula until just blended and uniform in texture.
05 - Once gelatin base is fully set, spread creamy topping evenly across surface using back of spoon or offset spatula.
06 - Return dish to refrigerator for at least 1 additional hour to allow layers to set together. Garnish with extra mandarin orange segments or orange zest if desired before serving.