Mix cornflakes cereal, confectioners' sugar, peanut butter, and butter together in a bowl. Scoop mixture using a melon baller into balls and arrange on a plate or baking sheet. Refrigerate until solid, at least 3 hours.
Place chocolate chips and oil in a microwave-safe glass or ceramic bowl. Heat in 30-second intervals, stirring after each interval, until melted, 1 to 3 minutes.
Grease a baking sheet.
Gently roll peanut butter balls in melted chocolate until evenly coated; arrange on the prepared baking sheet.