Despite Molly's invisibility, the characters still track her movements and make direct eye contact. They even react to her motions, like high fives and hugs, without verbal prompt.
Alex Désert played Eli Williams on the sitcom Boy Meets World (1993), whereas Rowan Blanchard is the star of the Boy Meets World sequel series Girl Meets World (2014). Désert played Cory Matthews' teacher and Blanchard plays Cory's daughter, Riley.
Paris Berelc is the fourth actress from a Disney XD series to star in a Disney Channel Original Movie, after Kelli Berglund in How to Build a Better Boy (2014), Spencer Boldman in Zapped (2014), and Olivia Holt (prior to starring in I Didn't Do It (2014) on Disney Channel) in Girl Vs. Monster (2012).
Based on the novel "My Invisible Sister" by Beatrice Colin and Sara Pinto.
Coug originally had a younger sister named Karen (Francesca Capaldi). Why she wasn't featured in the final film is not known.