Mariposa Diaz is Marco's baby sister who appears in the fourth and final season of Star vs. the Forces of Evil. While Marco was away on Mewni, Rafael and Angie decided to have another baby. Marco would not be aware of this until he and Star were invited to a baby-shower in "Marco Jr." At the time, they were expecting a boy, but turned out to be a girl once she was born. Mariposa is very close to her brother, and by "Gone Baby Gone" becomes friends with Meteora Butterfly.
- Her first name is Spanish for "butterfly".