1Line 13x9-inch pan with foil, leaving foil overhanging at 2 opposite sides of pan; grease foil generously with shortening or butter. In 3-quart saucepan, melt 1/4 cup butter over medium heat. Add marshmallows; cook 2 to 3 minutes, stirring frequently, until melted. Remove from heat; stir in peanut butter until smooth. Stir in cereal.
2Press mixture evenly in pan, using greased spatula or waxed paper. Sprinkle with chocolate chips; press gently into cereal mixture. Cool completely, about 30 minutes.
3Line cookie sheets with waxed paper. Use foil to lift bars out of pan. Cut into 6 rows by 3 rows. In microwavable bowl, microwave candy melts uncovered on High 1 minute or until melted; stir until smooth. Dip top of each bar into melted candy; smooth top with spatula. Sprinkle crushed cookies on top edge of dipped bars for “hair.” Place on cookie sheets. Firmly press pretzel pieces halfway into sides of each treat. Use frosting to attach 2 candy eyes to each face. Spoon remaining frosting into resealable food-storage plastic bag; seal bag. Cut off tiny corner of bag. Twist bag above frosting; squeeze to pipe frosting onto treats for “scars” and mouths.