Stir frozen, thawed raspberries with sugar until most of the shape of the raspberries disappears.
Or you can microwave them slightly to soften them.
If the raspberries are warm, place them in the fridge until chilled.
Stir ½ of the Cool whip into the raspberries until well combined, then gently fold the remaining cool whip into the raspberries.
Fold marshmallows, fresh raspberries, and Oreos into the raspberry mixture, then mix until just combined.
Cover and refrigerate for at least 1 hour before serving because the marshmallows and Oreos will soften a bit. Enjoy!