To start, crush about 75 vanilla wafers in a food processor to make crumbs. Place the vanilla wafer crumbs in a large bowl. Add pecans to the food processor and process until ground. Add the nuts to the bowl with the cookie crumbs.
To the bowl add powdered sugar and unsweetened cocoa powder and stir to combine.
In a separate bowl combine the rum, light corn syrup, and water. Add the rum mixture to the confectioners' sugar mixture and stir to combine. Shape into 1-inch balls then roll in additional powdered sugar, chocolate sprinkles, or wafer crumbs. Store in an airtight container and let chill for at least four hours before serving to bring out the rum flavor.