Start by preparing the fruit. Wash and slice the strawberries, and place them in a medium bowl. Add the blueberries and mini marshmallows to the bowl and gently mix until combined.
In another bowl, spoon in the whipped cream and set aside.
Take a sugar cone and fill the bottom with a layer of the fruit mixture, packing it down slightly.
Add a generous dollop of whipped cream on top of the fruit layer in the cone.
Continue layering the fruit mixture and whipped cream until the cone is filled to the top.
Repeat the process with the remaining sugar cones.
Garnish each cone with a fresh mint leaf if desired.
Serve immediately or refrigerate for up to 30 minutes before serving for a chilled treat.