- “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"
Eclipsa Butterfly (also known as Eclipsa the Queen of Darkness) is a character in the Disney XD animated series, Star vs. the Forces of Evil. She is the former ruler of Mewni and Star Butterfly's ninth great-grandmother.
Little is known about Eclipsa, but what is revealed indicates a dark and/or less-than-respectable reputation. In "Into the Wand", Star discovers more of her family history during her venture inside her wand. In a place what she called the "Grandma Room" were tapestries representing the past and present Queens of Mewni, including her mother. According to a passage inscribed on one of the room's pedestals, Eclipsa was wed to a Mewman king, but she was already in love with a monster with red skin, white hair, and four eyes. Eclipsa later eloped with this monster and abandoned the Mewni throne.
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 King 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, as she was among various interdimensional creatures that he imprisoned in crystal; however, upon closer inspection, she had managed to pull her right arm out of her glove. Her crystallize imprisonment kept her alive for three hundred years, and at some point met her eighth great-granddaughter, 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. At the end of The Battle for Mewni, part of Eclipsa's crystal prison cracked.
- Eclipsa has cheek markings shaped after a card suit, in this case hers are spades. She shares this trait with Star (hearts), Queen Butterfly (diamonds), and Miss Heinous (clubs).
- Eclipsa's voice is provided by Esmé Bianco who is best known for her recurring role as Ros in Game of Thrones.