In a large mixing bowl, combine the sour cream and dry instant vanilla pudding mix, whisking until smooth.

Gently fold in the thawed whipped topping using a rubber spatula until the mixture is uniform in color and texture.

Add the drained mandarin oranges, drained pineapple tidbits, and miniature marshmallows to the bowl.

Carefully fold the fruit into the cream base, taking care not to break the delicate mandarin orange segments.

Incorporate the shredded coconut if desired.

Cover the bowl with plastic wrap and refrigerate for at least 2 hours to allow the marshmallows to soften and flavors to meld before serving.