In a large bowl, combine crushed vanilla wafers, 1 cup powdered sugar, chopped nuts, and cocoa powder. Mix well until evenly distributed.
Add corn syrup and rum, stirring until the mixture comes together and is evenly moistened. It should hold together when squeezed.
Using a small cookie scoop or tablespoon, scoop out portions and roll into 1-inch balls with your hands.
Roll each ball in additional powdered sugar until completely coated.
Store in an airtight container in the refrigerator for at least 24 hours before serving to allow the flavors to develop. They'll keep for up to 3 weeks refrigerated or can be frozen for up to 3 months.