In a medium saucepan, whisk together the non-instant vanilla pudding mix, orange jello, and 3 cups of water until fully blended. Place the saucepan over medium heat and stir consistently until it reaches a rolling boil. Remove from heat and chill for 4-6 hours until set.

Transfer the chilled mixture into a large mixing bowl. Using a hand mixer or stand mixer, whip the mixture on medium speed for about 2-3 minutes until smooth and fluffy.

Gently fold in the Cool Whip until fully combined. Then, add in the mini marshmallows and the drained canned mandarin oranges, mixing carefully.

Cover with plastic wrap or a lid and let it chill in the refrigerator for about 30 minutes before serving.