Under The Sea: A Descendants Story is a live-action short-form special that premiered on September 28, 2018 at 7:40pm. Descendants stars Dove Cameron and China Anne McClain reprise their roles as Mal and Uma, respectively in the special which features the arch-nemeses facing off in an epic underwater showdown. Descendants 2 stars Thomas Doherty and Dylan Playfair reprise their roles of Harry and Gil, respectively, as part of Uma’s wicked pirate gang.
Mal walks to the beach after she encounters her father in the mystical forest. Dizzy walks by and tells Mal about hair makeovers. But, a glowing magic comes from Uma's necklace that she's wearing right now then makes an evil smirk and tells Mal that's she's coming for her. Mal then jumps down underwater and battles Uma who curses Dizzy then eventually wins. Then the whole battle was all just a dream by Mal and Dizzy wakes her up. Mal explains the whole dream to Dizzy before Dizzy tells her to have a makeover whatever she likes. The call of Mal's Father was heard and was coming from Auradon. While Dizzy and Mal leaves Uma's necklace is left on the ground and Uma's voice says that danger is coming for Mal. Which will presume that the danger is foreshadowing Descendants 3.
- Mini-movie includes the song "Stronger" performed by Dove Cameron & China Anne McClain (Kelly Clarkson’s cover). It is available in official music video clip with SFX (3:21); and longer clean audio-version (4:15).
- Dove Cameron as Mal, daughter of Maleficent
- China Anne McClain as Uma,daughter of Ursula
- Thomas Doherty as Harry Hook, son of Captain Hook
- Dylan Playfair as Gil, son of Gaston
- Anna Cathcart as Dizzy Tremaine, daughter of Drizella Tremaine