With Guardians of the Galaxy Holiday Special revealing Mantis and Star-Lord as siblings, it looks like James Gunn has decided to deviate even further from the source material. But can we blame him, because the scene of the revelation itself was one of the most heartwarming scenes in the Marvel Cinematic Universe, and it did fit the story.
Guardians of the Galaxy Holiday Special isn't the first time Gunn has deviated away from the comics. With Star-Lord now having a sister in Mantis, it breaks the established lore in comics and makes for some good dramatization.
Mantis and Star Lord's relationship explored as Guardians of the Galaxy Holiday Special reveals them as siblings
In the comic books, Mantis joins the Guardians of the Galaxy when she helps them defeat the Phalanx, a techno-organic transmode virus. She and Peter Quill have a frenemy element to them as she helps him manipulate the team. She would however join Rocket's offshoot group when the team realized that Peter used her to manipulate them.
She would also help the team save Earth-616 from the "Cancerverse," which saw Death die in their universe and caused their undying inhabitants to become monstrous entities. However, in the films, this is not how it goes considering Mantis and Peter Quill are never really siblings in the comic books.
In Guardians of the Galaxy Vol. 2, Mantis meets up with the team when she is a counselor to Ego. While the film doesn't outright confirm that they are siblings, there are hints dropped here and there. While Ego had many children throughout the universe and had them killed because they wouldn't join his genocidal plan, Mantis was the only one he wouldn't kill because she was able to put him to sleep.
Her relationship with Quill, though, was already confirmed in a deleted Instagram post that was put up by the actress who played Mantis' mother in the film. With Guardians of the Galaxy Holiday Special, this information gets confirmed outright in the opening moments, as it is what fuels most of her journey.
Concerned with making Peter have the best Christmas ever, she went to Earth and kidnapped Kevin Bacon so that she could give Peter the best present to date. However, things didn't go according to plan, as Star Lord didn't like Bacon's kidnapping and ordered Guardians to send him back to Earth. Bacon, however, suggested that he would stay back, and he went on to deliver a concert that brought about the Christmas spirit.
It's over here where we get the heartfelt scene between Peter and Mantis as she reveals that she is his sister, which leads to him embracing her as family. It's a sweet development, and did do great for the growth of these characters. Though it's worth noting that neither of them has any siblings in the books.
You can check out Mantis and Quill next when Guardians of the Galaxy Vol. 3 releases next May.