Big Boing

Big Boing, know as Lady Susan in the English dub, is a member of a league of American superheroes apparently led by Dr. Riddles, The Majestic Twelve. Her power includes bouncing her enormous breasts up and down or shaking them with her arms to distract everyone. She is the most prominent of the 12, appearing occasionally on her own and consistently seen alongside Dr. Riddles. She also, on occasion, is shown as actually able to fight. Her dialogue consists almost exclusively of the word "yay".

(Source: Wikipedia, edited)