Under the Sea: A Descendants Story, on Disney Channel
Disney Wiki; IMDb; Wikia
streaming sites: Disney+; YouTube

This is a 9-minute special that takes place between "Descendants 2" and "Descendants 3." It aired on September 28, 2018, but I didn't see it until 2021, on Disney+. Mal emerges from a forest on the Isle of the Lost, and meets Dizzy on the shore. But Dizzy turns out to be possessed by Uma, via her necklace. Uma makes some threats, as do Harry and Gil, after they show up in person. Then Mal jumps into the sea and there's this whole music video, before Mal appears on the shore again, talking to Dizzy, who is no longer possessed. It's all pretty weird and doesn't really make much sense, though I suppose it might be more meaningful to me after I see the third movie. I dunno, and I don't really care either way. But I'm glad to have seen the special, I guess, just for the sake of being complete about watching the franchise, or whatever.