Sora, Donald, and Goofy arrive on this strange new world after being given new magical forms by Donald that will allow them to survive and adapt. They quickly meet up with Ariel (Halle Bailey), Flounder (Jacob Tremblay), and Sebastian (Daveed Diggs). After teaching them to swim, the group is attacked by a group of Heartless, which Sora and his gang promptly dispatch. A concerned Ariel invites the group to visit her father's palace to see what to do. Taking them there, Triton (Javier Bardem) dispatches more Heartless with his magic trident, dismisses Sora's questions about the world's Keyhole, and grounds Ariel. Sulking, Ariel sneaks off to her grotto, where she points out a mysterious mark on the wall. The party travels to the Sunken Ship, where they find a shining Crystal Trident that looks as if it might fit in the mark. After escaping Glut, they take it back to the Grotto and place it on the wall, but before it can activate, Triton bursts in and destroys it. Ariel storms off, allowing Triton the opportunity to explain that he knows Sora and the rest are Keyblade bearers from another world. After proclaiming the Keyblade only brings destruction, he informs them they have no further business in Atlantica. Meanwhile, Ariel is approached by Ursula (Melissa McCarthy), who promises the mermaid princess that she can help her get to "other worlds", but in order to do so, she needs Triton's trident. Ariel steals it and gives it Ursula, who uses it to injure Triton before retreating to her lair. Sora, Donald, and Goofy go in pursuit. Ursula escapes from her lair, but Ariel gives Sora a new power that will help him and the party get to Ursula and defeat her for good. Ursula receives a swift kick in the tentacles from Sora and his gang; they return the trident to Triton. He and Ariel open up the world's Keyhole, which Sora promptly seals.
