In a medium bowl, whip the heavy cream with an electric mixer until soft peaks form. Gradually add the powdered sugar and vanilla extract, continuing to whip until stiff peaks form. Set aside.
In another bowl, prepare the vanilla pudding according to package instructions if not already prepared.
Take the mini graham cracker cups and fill each one with a layer of vanilla pudding, about 2 tablespoons per cup.
Add a layer of mixed berries (strawberries, blueberries, and raspberries) on top of the pudding, filling each cup about halfway.
Spoon a layer of whipped cream over the berries, filling each cup to the top.
Repeat the layers if your cups are deep enough, starting with pudding, then berries, and finishing with whipped cream.
Garnish each trifle with a mint leaf if desired.
Chill the trifles in the refrigerator for at least 30 minutes before serving to allow the flavors to meld.