In a microwave or in a large saucepan over low heat, melt marshmallows in oil; stir until smooth. Remove from heat; stir in cereal, 2/3 cup each caramels and pretzels. Press mixture into a lightly greased 13x9-in. baking pan using waxed paper or a lightly greased spatula. Cool to room temperature. Spread melted chocolate over top; sprinkle with remaining caramels and pretzels. If desired, sprinkle with sea salt. Cut into bars.