In a medium bowl, whisk the instant vanilla pudding mix and cold milk for two minutes until the mixture begins to thicken.
Gently fold the thawed whipped topping into the pudding mixture until just combined. Do not overmix.
Carefully fold in the blueberry pie filling, miniature marshmallows, and fresh blueberries. Mix until the ingredients are evenly distributed.
Cover the bowl and chill the blueberry fluff salad in the refrigerator for at least two hours before serving. This allows the flavors to meld and the salad to set properly.
Serve cold as a sweet, creamy blueberry dessert salad.
Notes
For a firmer texture, you can substitute the instant vanilla pudding mix with a sugar-free version, though the chilling time may need to be slightly extended.
You can prepare this light and airy blueberry salad up to 24 hours in advance. Keep it covered in the refrigerator.
If you do not have fresh blueberries, you can use an additional half can of blueberry pie filling instead.