- “Eclipsa Queen of Mewni to a Mewman King was wed, but took a monster for her love, and away from Mewni fled.”
- ―Pedestal in the Butterfly Castle "Grandma Room"
Little is known about Eclipsa, but what is revealed indicates a dark and/or less-than-respectable reputation. In "Into the Wand", a tapestry of Eclipsa is shown among the past and present Queens of Mewni. According to a passage inscribed on the tapestry's pedestal, Eclipsa was wed to a Mewman king, but she was already in love with a monster named Globgor. Eclipsa later eloped with this monster and had a Mewman/monster hybrid child named Meteora (the true identity of Miss Heinous), who was switched with a peasant child, Festivia, by the Magic High Commission.
During her life, Eclipsa developed a number of spells that were associated with dark magic. These spells were recorded in the pages of the wand's Magic Instruction Book and sealed behind a skull-shaped lock to prevent others from reading them. She was also the only member of the royal family who never questioned Glossaryck's teaching methods. According to Baby, Eclipsa had a very high affinity for magic compared to the other queens, rivaled only by Star herself. It is also presumed from a remark by River Butterfly that Eclipsa harbored sympathy for Mewni's monsters, a sentiment shared by very few of her fellow Mewmans and royals. At some point before the events of "Crystal Clear", Eclipsa was apparently encased inside a crystal by Rhombulus. Her crystallize imprisonment kept her alive for three hundred years, and at some point met Moon Butterfly. Rhombulus briefly unfreezed part of her body so Moon could ask Eclipsa for a spell that could defeat Toffee. Eclipsa was willing to help, but in return wanted her freedom once her enemy was destroyed.
Eclipsa is portrayed as calm, approachable, and sympathetic, despite her reputation as a queen of evil. (She was only branded such because of her extreme "outside the box" beliefs. Even the Magic High Commission admitted to sealing Eclipsa in crystal "before she could do anything [evil]"; even though Eclipsa's only crime by law was abandoning her arranged husband King Shastacan.) She bears no ill will towards her jailers, despite her long time in crystal captivity, and displays a carefree, fun-loving attitude similar to Star. She maintains her calm demeanor further on in the series, and is more than willing to help Star whenever she is troubled. She also has a fondness for chocolate bars and roses.
Eclipsa has short, poofy teal hair, grayish-purple eyes, pale skin, and red spade-shaped marks on her cheeks. She wears a long, dark purple Gothic-themed dress, a large black sun hat with gray and white feathers and a thorny branch, a white cravat with a lavender crescent moon on it, and gray opera gloves. Eclipsa also has maroon-colored lipstick and black mascara. Underneath her gloves, her hands are dark purple with purple veins sprouting out on her arm.
Role in the series
At the end of "The Battle for Mewni", Moon checks on Eclipsa's prison after Toffee was defeated by Star. When the prison seems intact, Moon leaves; but right after, part of Eclipsa's crystal prison cracks. It is later revealed that at some point before "Stranger Danger" Eclipsa escaped from the crystal prison and traverses to the royal family's garden. She meets Star (along with a reborn Glossaryck), and the two strike up a friendship. However, Eclipsa is discovered by the Magic High Commission who imprison her and sentence her execution. Seeing Eclipsa as a victim instead of truly villainous, Star convinces them to give Eclipsa a fair trial. Afterwards, Eclipsa is put under castle arrest until her trial, and currently resides in an old tower which used to be her room. Throughout the first half of season three, Star often turns to Eclipsa for advice whenever she is troubled. Eclispa helps Star with her troubles concerning Marco, who decided to live on Mewni. When Star tells her that she made him a squire for the Knight of the Wash, Eclipsa warned her that attending the laundry was the most dangerous job in the castle, prompting Star to rescue Marco. When Star discovers that she can travel through multiple dimensions in her dreams, Eclipsa encourages her to embrace them instead of running away from them.
Before her trial took place, Moon reluctantly looked into the history of the Butterfly family, after Star discovered that Miss Henious was Eclipsa's daughter. Eclipsa helped Moon get into the Royal Archive in the Bureaucracy of Magic and discovered that all history on her daughter had been erased and replaced with Festivia. Certain that the Magic High Commission was keeping secrets from the royal family, Eclipsa, Moon, and Star set-up a rigged trial to force the Commission to reveal the truth. Using the truth or pain game, the Commission confessed they replaced Meteora with Festivia and erased all recorded history of her existence. This also confirmed that all of Festivia's descendants, including Moon and Star, were not true-blooded members of the Butterfly family.
- Eclipsa has cheek markings shaped after a card suit, in this case hers are spades. She shares this trait with Star (hearts), Moon (diamonds), and Meteora (clubs).
- Eclipsa's voice is provided by Esmé Bianco who is best known for her recurring role as Ros in the hit HBO series Game of Thrones.
- Eclipsa was the most open-minded queen of the true royal line, as she saw monsters as equals and fell in love with Globgor.
- Eclipsa was imprisoned, not because she was an actual threat, but out of fear and prejudice by the Magic High Commission.
- Much like how Toffee had beliefs similiar to Magneto, Eclipsa's beliefs are similar to Professor X, who believed in peace between different species.
- Eclipsa's magic is an homage to Sailor Pluto from Sailor Moon.