Line large cookie sheets with cooking parchment paper.
In medium microwavable bowl, add cereal.
In small microwavable bowl, microwave 2 tablespoons butter uncovered on High 20 to 30 seconds or until melted.
Stir in 1 tablespoon sugar; microwave about 30 seconds or until sugar is nearly dissolved.
Pour butter mixture over cereal, mixing to coat.
Microwave uncovered on High 2 to 3 minutes, stirring every 30 seconds, until glazed and toasted.
Spread mixture on waxed paper; cool 10 minutes.
Place cereal in large resealable food-storage plastic bag, and coarsely crush; set aside.
Meanwhile, in small bowl, mix flour, baking soda and salt; set aside.
In large bowl, beat softened butter, brown sugar and 3/4 cup granulated sugar with electric mixer on medium speed, or mix with spoon until well mixed; scrape side of bowl.
Beat in egg until blended.
Beat in vanilla.
Stir flour mixture into butter mixture until well mixed (dough will be stiff).
Stir in crushed cereal, chocolate chips, marshmallows and oats.
Shape into 40 (1 1/2-inch) balls.
Place 2 inches apart on cookie sheets.
Flatten slightly, reshaping edges if necessary to make round.
Cover balls lightly with plastic wrap while waiting to bake.
Baking one cookie sheet at a time, bake 8 to 10 minutes or until edges are set (centers will be soft).
Cool completely on cookie sheet, about 15 minutes.