Plot
City girl Ronnie Anne Santiago celebrates her twelfth birthday. She intends to celebrate her "Summer of 12" at Xtreme Eddie's with her best friend, Sid Chang, but her family surprises her with a trip to Japunda, Mexico, much to her dismay. In Mexico, Ronnie Anne takes interest to a necklace that a shopkeeper claims to hold the last connection between humans and gods, but Maria dismisses it as a hoax. However, Ronnie Anne buys the necklace behind her mother's back.
The family head to their Mama Lupe's house, where Ronnie Anne points out a nearby mountain that resembles a half-pipe. Carlos Sr. tells her that the mountain is named after the petrified form of the demigoddess Punguari, whose parents denied her from becoming a full-fledged god due to her rebellious nature and lack of responsibility. Dissatisfied, Punguari snuck out and stole a mask that allowed her to become a god; however, the ground around her started to crack and separate. Sisiki, her mother, was forced to petrify her daughter; should Punguari be freed now, Mexico would be in danger.
The next day, Ronnie Anne decides to go to Mount Punguari, where she starts to synchronize skate with Sid over video call. However, Ronnie Anne falls off her skateboard, breaking her necklace and releasing Punguari. Soon, a young girl, who introduces herself as Shara, calls for help, her leg having been trapped underneath a branch following an earthquake. Ronnie Anne, accompanied by Shara, is confronted by her mother, who is angry that she snuck out to do her own thing. Later that evening, Maria expresses her frustration about Ronnie Anne's rebellious nature, prompting Mama Lupe to take her outside to practice her chancla throwing.
Shari and Ronnie Anne sneak away to a museum, where Ronnie Anne uncovers the gateway to the realm holding the mask. Shari, taking the mask, reveals that she is in fact Punguari all along, leaving Ronnie Anne trapped within the realm. However, her grandfather Hector ends up finding her through a magical mirror. Ronnie Anne explains her plight to her family, who sneak into the museum at night to save her. Ronnie Anne realizes that the story of Punguari was wrong: as Punguari wielded the mask, the cracks forming within the ground was allowing another deity - Ucumu, the god of the underworld - to rise up from the ground.
Punguari harnesses the mask's power to make her a god, draining the sea and creating a temple in its wake. However, the earth starts to crack once more. Ronnie Anne decides to go to Punguari's temple herself, where she confronts Punguari and tells her the true story: her parents petrified her to protect her from Ucumu. They notice that Maria, who tried to get to the temple, is about to slip into the newly-formed cracks. Punguari shapeshifts into a coyote and runs toward Maria, who uses her itinerary to swing herself to safety. The family and Punguari regroup as Ucumu rises from the cracks.
Ronnie Anne rides off with Punguari into battle, while Maria orders Lalo, the family dog, to dig for a giant chancla, and Bobby grabs the sacred flame housed beneath Mama Lupe's house. Bobby's group returns to the mainland as Ucumu summons a group of minions to attack. Lupe's housekeeper Don Tacho crashes the plane he was piloting into the minions, taking them out, and each Casagrande utilizes their strengths to fight them off. Punguari is eventually knocked out by Ucumu, who proceeds to drag her into a skull on his mask.
Maria, aided by a group of Chancla Warriors, is able to lift the giant chancla long enough for Frida to knock a paper cutout of Arturo, which is engulfed in the sacred flame, into the chancla, which strikes Ucumu, reducing him into a skeleton. Ronnie Anne fires at Ucumu, destroying him and petrifying all of his minions. Punguari seals the cracks using the temple she built, preventing Ucumu's return, and reunites with her parents, who had been turned into gemstones. Sisiki and Maria reconcile with their respective daughters and put aside their differences.
Punguari's father, Chipiri, restores the mainland back to its former glory, and the Festival of the New Fire is now being held at Mama Lupe's island. Maria presents her daughter with another gemstone as Punguari, Sisiki and Chipiri watch the celebrations from afar.
