Place half of the mint leaves in the bottom of a large pitcher. Use a muddler or the end of a wooden spoon to press gently all over the mint for about 30 seconds (this helps the mint release its tasty essential oils). Add the remaining fresh mint, the rum, lime juice, berry syrup, club soda, and stir to combine. Add the lime slices and ice and serve immediately. Makes 12 servings.
PS: The color of your berry mojito will vary depending on the berries you use. I used mostly raspberries with a few blackberries and blueberries.