Meteora

Princess Meteora Butterfly, also known as Miss Heinous, is the Mewman/monster hybrid daughter of Queen Eclipse and the former headmistress of St. Olga's Reform School for Wayward Princesses. She first appears in the episode of the same name. In the latter part of Season 3, Meteora rediscovers her true parentage and background and plots to take the throne of Mewni from the Butterfly family. In the finale episode "Conquer", she is reverted back to infancy following her defeat at the hands of her mother Eclipsa. She is voiced by Jessica Walter.

Personality
When first introduced, Miss Heinous wants to strictly control bad behavior in wayward princesses, forcing them to act like "proper" princesses with no individuality of their own.

Toward the end of her debut episode, Miss Heinous struggles to contain her individuality once she loses control of her emotions, and club-shaped marks appear on her cheeks.

In her first appearance, she had a habit of second-guessing her choices of words, questioning whether they were appropriate for the situation.

In her third appearance, Miss Heinous has been shown to have become deeply unhinged, desiring gruesome vengeance against Marco, and even wanting the entire multiverse to fear her. She also seems to have developed a motherly attachment to Rasticore, coddling his regenerating arm.

In "Monster Bash", Miss Heinous starts to remember her original identity after seeing her old nursery and insists that Gemini refer to her as Meteora.

"Skooled!" shows that Meteora suffers from some abandonment issues, demonstrated from the way she reacts to Rasticore's attempt to quit his job as her bodyguard. This may be the result of her particular upbringing by the robotic headmistress St. Olga.

From "Tough Love" onward, Meteora becomes obsessed with reclaiming her birthright of the throne of Mewni, being willing to crush anyone who tries to stop her. She has even grown more mentally unstable, becoming cruel and sadistic without a care of destroying the very kingdom she sought to reclaim.

Biography
As the headmistress of St. Olga's Reform School for Wayward Princesses, Miss Heinous makes sure her staff has the princesses attending her reform school reformed into "normal" princesses. For particularly troublesome princesses, she uses the "Solitary Conform-ment Chamber", which forcibly brainwashes them into acting the way she wants them to.

Despite her best attempts, Star Butterfly and Marco Diaz infiltrate the school and cause a revolt. After they leave, she finds out via experimenting with a bobby pin Marco dropped that they came from Earth, and swears to annihilate them.

In "Goblin Dogs", Pony Head reveals that Miss Heinous has left St. Olga's.

In "Gift of the Card", Miss Heinous is seen living with her assistant Gemini in a rundown apartment complex, with very little money. She hires Rasticore Chaosus Disastervaine to find and destroy Star and bring Marco to her as revenge for what they did to her. However, Rasticore fails, and his forearm is delivered back to Miss Heinous, to her displeasure.

In "Heinous", she, along with Gemini and Rasticore's slowly regenerating arm, comes to the Diaz Household, informing Marco's parents that he has wronged her. After a brief negotiation, she is able to convince them to allow her to punish him by filming a video for the rebel princesses Marco inspired where he renounces the words he used to incite the revolt. Despite Marco saying this in a deeply sarcastic way, Heinous is satisfied with the results and departs. That night, as she prepares to sleep inside her car, she talks to Rasticore's arm, telling it she will annihilate Marco and Star, and make the multiverse "shiver in fear" of her. As she says this, she removes the makeup used to hide her cheek symbols.

In "Princess Turdina", Miss Heinous returns to the school in an effort to get control back. She reveals to her former students that the "Princess Marco" they idolize is a boy, and she also says she needs them just as much as they need her. However, the students chase her off once again, and she starts using princesses as fuel to restore her youth.

In "Monster Bash", Miss Heinous tries to steal Marco's youth, but ends up becoming part of a conflict between Star and Mina Loveberry, during which she is revealed to be Meteora Butterfly, the half-breed daughter of Queen Eclipsa and her monster lover. In "Total Eclipsa the Moon" and "Butterfly Trap", it is further revealed that she was replaced by the peasant girl Festivia as Eclipsa's daughter and heir after her mother was imprisoned, and all evidence of her existence was erased from royal records.

In "Skooled!", Meteora once again invades the school, this time to discover what happened to her when she was a baby. After confronting and destroying her adoptive mother St. Olga, ripping off Pony Head's horn, tearing out Gemini's robotic heart and blowing up Rasticore's body, she sets out to reclaim the throne of Mewni for herself.

In "Tough Love", Meteora goes on a destructive and soul-stealing rampage across Mewni in her efforts to seize the Mewni throne. Moon and Eclipsa confront her and try to reason with her peacefully, but when that fails, she attacks Moon, leaving her in a vulnerable state, and flees.

In "Divide" and "Conquer", Meteora invades Butterfly Castle in a mad attempt to seize control from acting queen Star Butterfly, eventually succeeding in stealing the souls of everyone on Mewni except Glossaryck, Star and Tom Lucitor, who is somewhat immune to her soul stealing gaze due to having thousands of them. After a furious battle against Star, Meteora is defeated when her own mother Eclipsa uses the magic wand to revert her back to a baby.

Role in the series
Since her defeat, Meteora continues to remain an infant to be properly raised by Eclipsa and Globgor. Queen Moon claims that Meteora is a destructive baby when she and Star are babysitting her.