Complex sentence: However, they discover a "Parental Revenge Center" hotline with guaranteed results, which is run by Cartmen who agrees to help the two.However, Cartman's revenge plan for both boys involves going to both of their houses to smear all of the walls with feces.
Split into simpler sentences: However, they discover a "Parental Revenge Center" hotline with guaranteed results, which is run by Cartmen. Sadly, Cartman's revenge plan for both boys involves going to both of their houses to smear all of the walls with feces.