If you looking of the episode of the same name? See The Precious, Wonderful, Adorable, Lovable Duckling (episode)
He also tried to dispose of Muriel in many cruel ways so he can eliminate competition for Eustace's affections, and was greatly angered each time Muriel escaped thanks to Courage, or Muriel did something kind to Eustace. The mean Duckling is the minor antagonist of the show. The duck sees Eustace as his "Momma," which is Ironic, given the fact Eustace wanted to eat his egg at the beginning.