In a large mixing bowl, combine the crushed vanilla wafers, 1 cup powdered sugar, chopped nuts, and cocoa powder. Mix well until evenly distributed.
In a small bowl, whisk together the corn syrup and rum until well combined.
Pour the liquid mixture over the dry ingredients and stir with a wooden spoon or your hands until everything is moistened and holds together when pressed.
Roll the mixture into 1-inch balls using your hands. If the mixture is too sticky, lightly dampen your hands with water.
Place additional powdered sugar in a shallow bowl and roll each ball until well coated.
Store in an airtight container at room temperature for at least 24 hours before serving to allow flavors to meld. They'll keep for up to 3 weeks or can be frozen for up to 3 months.