‘Agatha All Along’ fan theory suggests Rio Vidal is the child of an iconic Marvel villain

Agatha All Along recently enjoyed its two-episode premiere, and some viewers are convinced that Rio Vidal (Aubrey Plaza) has ties to one of Marvel Comics’ most iconic villains.

The series is a spinoff of WandaVision and follows Agatha Harkness (Kathryn Hahn) after a mysterious Teen (Joe Locke) helps her break free from the spell Wanda Maximoff (Elizabeth Olsen) put her under. Free from the spell, Agatha begins forming a new coven of witches. However, her return to her old life means she also has to face some demons from her past, including Rio.

Rio is a powerful Green Witch who quickly reveals her intentions to kill Agatha. Although it’s not clear why she seeks revenge on Agatha, it’s implied the pair have a shared history and may have even been lovers once.

Rio is an especially interesting character because she’s not in Marvel Comics. Instead, she is an original character designed specifically for the show—at least, she was marketed as such. After the first two episodes, though, viewers believe Agatha All Along is hinting that there’s more to Rio’s identity.

Is Agatha All Along setting the stage to introduce a huge Marvel villain?

A fan theory has arisen that Rio is actually the daughter of Mephisto, one of the greatest supervillains in Marvel Comics. He is an immortal demonic entity that rules over the pocket dimension called Hell and boasts very powerful magical abilities.

For years, fans have been petitioning for Mephisto to make his MCU debut, making it quite exciting that Rio could be proof of Mephisto’s existence in the MCU. In the comics, Mephisto has several children, and Agatha All Along may be teasing that Rio is a gender-swapped Blackheart.

The main reason for the theory is that the show has referenced “black hearts” twice in just the first two episodes. In the first episode, Rio and Agatha battle each other, with Agatha commenting that Rio doesn’t have a heart. Rio corrects her, stating, “Yes, I do. It’s black.”

In the second episode, Agatha and Teen find Lilia Calderu (Patti LuPone), a witch with divination skills. She uses her abilities to conjure a list of the witches meant to be a part of Agatha’s coven. The list includes four names, although Agatha initially denies this and claims there are only three. Later, Lilia confirms that there wasn’t a fourth name. In place of a name, a single black heart was drawn to symbolize the fourth person in the coven.

Agatha ends up recruiting Mrs. Hart (Debra Jo Rupp) as the fourth member. However, it’s quite clear that the heart meant Rio was supposed to be the fourth member, even though Agatha refused to invite her. One can’t help but wonder if the references to Rio’s “black heart” have a deeper meaning.

In the comics, Blackheart is Mephisto’s son, conjured from dark energy. Blackheart is banished to Earth by his father but eventually returns to Hell to destroy Mephisto and take over his realm. Rio’s chaotic, vengeful, and heartless villain would be a good fit for Mephisto’s estranged daughter in the MCU.

It remains to be seen if Rio really is Blackheart, but if so, Agatha All Along could be paving the way for Marvel’s most anticipated supervillain to enter the MCU.