Prepare the Berries
Wash strawberries and blueberries under cold running water and pat completely dry with paper towels.
Remove green tops from strawberries and dice into small, bite-sized pieces (about half an inch). Leave blueberries whole.
Make the Cheesecake Base
In a large mixing bowl, beat room temperature cream cheese with a hand mixer on medium speed until smooth and fluffy, about 1 minute.
Gradually add powdered sugar in three batches, mixing until completely incorporated and creamy.
Add vanilla extract and mix thoroughly.
Fold in the Whipped Cream
Add whipped cream to the cream cheese mixture.
Using a rubber spatula, gently fold together with smooth, sweeping motions until smooth and uniform with no streaks visible.
Combine Everything
Gently fold in mini marshmallows until evenly distributed.
Add diced strawberries and whole blueberries to the bowl.
Fold everything together with gentle motions to avoid crushing the berries, ensuring even distribution.
Serve
Transfer to a serving bowl immediately or cover tightly with plastic wrap and refrigerate.
Garnish with extra fresh berries just before serving.
Serve chilled.