Meteora Butterfly

Miss Heinous the tertiary antagonist of Star vs. the Forces of Evil. She is the headmistress of St. Olga's Reform School for Wayward Princesses and is the arch-enemy of Marco Diaz. In her school, she "reforms" rebels princesses and makes them act like "proper" princesses with no individuality of their own.

After losing control of her school due to the actions of Marco Diaz and Star Butterfly, she swears revenge upon them and seeks to destroy them at all costs. In "Monster Bash" she is revealed to be Meteora Butterfly, the Mewman-monster hybrid daughter of Queen Eclipsa.

Trivia

 * According to Star and Marco's Guide to Mastering Every Dimension, Miss Heinous is an interdimensional fugitive wanted by the Magic High Commission.