Heat a medium saute pan over medium heat. Add cranberries, granulated sugar, and water. Bring to a boil, then reduce heat and simmer for about 10 minutes, or until berries begin to burst. Remove from heat and pour cranberries into a bowl. Cover with plastic wrap and cool completely. Refrigerate until ready to use.
In a large mixing bowl, gently stir chilled cranberry sauce, mandarin oranges, crushed pineapple together. Stir in mini marshmallows. Fold in whipped topping until all is coated.
Pour into a serving dish and chill until ready to serve.
If desired, top with a garnish of choice.