BEAT peanut butter and sugar in large bowl with mixer until blended. Add 1/2 cup wafer crumbs; mix well.
DROP tablespoonfuls of peanut butter mixture into 28 mounds onto waxed paper-covered baking sheet. Top each with 1 marshmallow; shape peanut mixture into ball around marshmallow to completely enclose marshmallow. Roll in remaining wafer crumbs until evenly coated, gently pressing crumbs onto balls to secure.
REFRIGERATE 4 hours or until firm.