Slice cake into 3 layers. Mash the strawberries in a bowl and fold in the Cool Whip. Spread a small amount of strawberry frosting on bottom cake layer then sprinkle with blueberries. Repeat steps with another layer.
Place top layer on cake. Mix the mini marshmallows into the remaining strawberry frosting.
Cover cake with the strawberry marshmallow frosting. Top with more berries.