Barbie: Mermaid Power

In the underwater kingdom of Pacifica, 8 mer-persons are selected by a beam of light emanating from a giant golden pearl to become its guardians. However, only 6 of them are present initially, prompting Isla to explore and find the missing two, who turn out to be the Malibu and Brooklyn Barbie characters.

Using a pearl necklace given by Isla, the Barbie-girls and Malibu Barbie's sisters—Skipper, Stacie, and Chelsea—transform into mermaids. Skipper and Stacie experience mermaid life for the first time, while Chelsea has previously encountered mermaids in her own series, Barbie: Dreamtopia.

Malibu Barbie begins to learn that the myth of mermaids is true as she explores her new abilities and the underwater world around her, realizing the reality of her mermaid heritage.

At a science academy, Marlo, returning from Dolphin Magic, attempts to prove the existence of mermaids to skeptical attendants. She faces doubt and rejection from the institution's leader, Dr. Amy Tang, who revokes her funding, dismissing her research as a 'frivolous fairy-tale witch-hunt.'

Marlo meets Isla, who explains that the girls are destined to gain powers and meet Pacifica's leader, Coralia. The mermaids will later face three competing contenders for the title of 'Power Keeper,' including Talluyah, Sareena, and Finn.

The girls encounter three antagonistic contenders for the 'Power Keeper' title—Talluyah, Sareena, and Finn. Finn's sister, Aquaryah, has several adventures with Chelsea, with Marlo's help and interference from her carnivorous fish-like creatures, which Chelsea and Aquaryah eventually outsmart and escape.

Barbie faces a submarine crash and other unexpected troubles that lead her to seek help from Marlo. With her assistance, Barbie finally obtains her water powers after witnessing her sisters and new friends using their abilities.

The mermaid girls use their newfound powers to confront and clear a mountain island of trash and filth, which threatened to harm Pacifica and the entire aquatic ecosystem. Their collective efforts prevent environmental disaster.

Aquaryah and Chelsea reunite with the Pacifica inhabitants, and Malibu Barbie recognizes Aquaryah as the 'Power Keeper' due to her bravery, kindness, and dedication. Barbie and her sisters then channel their powers to assist in the cleanup.

The mermaids and the Pacifica residents celebrate the successful preservation of their underwater environment. The film concludes with a joyful final shot of the characters posing together, marking their victory and unity.