Add the orange gelatin mix and 1 cup hot water to a large bowl. Whisk until the gelatin is completely dissolved.
Stir in ½ cup cold water.
Refrigerate for 15–20 minutes, or until the mixture begins to thicken slightly.
Remove from the refrigerator and whisk in the instant vanilla pudding mix until smooth.
Refrigerate for another 15–20 minutes, or until slightly thickened.
Fold in the thawed whipped topping until evenly combined.
Gently stir in the drained mandarin oranges, well-drained crushed pineapple, and mini marshmallows.
Cover and refrigerate for at least 2 hours before serving.
Serve chilled.
Notes
Drain the mandarin oranges and crushed pineapple thoroughly to prevent the salad from becoming watery.For the best texture, allow the salad to chill for at least 2 hours before serving.Store leftovers covered in the refrigerator for up to 3–4 days.