In a large mixing bowl, dissolve the strawberry gelatin in 2 cups of boiling water, stirring continuously for about 2 minutes until completely dissolved.
Add the partially thawed strawberries to the hot gelatin mixture. Stir gently until the strawberries begin to break down slightly.
Refrigerate the mixture for 30-45 minutes or until it reaches a soft-set consistency similar to egg whites. The mixture should be wobbly but not fully firm.
While the gelatin mixture chills, thoroughly drain the crushed pineapple using a fine-mesh strainer, pressing with the back of a spoon to remove excess moisture.
In a separate large bowl, fold together the thawed whipped topping and sour cream until fully combined.
Once the gelatin mixture has partially set, fold in the drained pineapple and miniature marshmallows, ensuring even distribution.
Gently fold in the whipped topping/sour cream mixture using a rubber spatula with a light hand. Use a bottom-to-top motion rather than stirring to maintain the airy texture.
Transfer the completed fluff to a decorative serving bowl or a 9x13 inch dish.
Cover with plastic wrap and refrigerate for at least 4 hours, though overnight chilling yields the best texture and flavor.
Before serving, garnish with fresh strawberries if desired.