In a large bowl combine orange Jell-O and boiling water. Whisk until Jell-o is dissolved.
Add cold water and allow to chill for 15 minutes in refrigerator. Slowly whisk in vanilla pudding mix until smooth and chill for another 15-20 minutes or until it becomes slightly thickened.
Fold in Cool Whip, mandarin oranges and marshmallows. Chill for at least 1 hour.
I like to let this jello sit for at least one hour before serving. You can most certainly make this recipe the day before a gathering. I brought this creamsicle fluff to a morning playdate and everyone loved the recipe!
You can top individual servings in ramekins with a little mandarin orange and mini marshmallows to make a perfect Easter or Mothers Day brunch place setting.