Madame Mildred Blubbery is the main antagonist of the episode "Opera Yumi", she is the former opera teacher of Yumi Yoshimura.
She is voiced by Katie Leigh.
When Yumi was a baby, she had a talent to sing opera, which amazed Blubbery. Blubbery raised her until Yumi quit opera by throwing a hissy fit, and left. Madame Blubbery found Yumi in the arcade with Ami after hearing her opera scream.