Dolphin

The Dolphin is found in Atlantica in Kingdom Hearts and Kingdom Hearts II. Flounder calls them "giant fish." It gives Sora and his party a ride past the currents that block the passage to the Shipwreck. The Dolphin in the Undersea Valley will be available even if there are Heartless but the player will be unable to ride the Dolphin until the Heartless are defeated.

Kingdom Hearts
During Sora, Donald, and Goofy's first visit to Atlantica, Dolphin can be seen swimming around in several places. The Dolphin helps the party to reach the Shipwreck, particularly when Sora does not yet have access to the Mermaid Kick ability. It also leads Sora to other places in Atlantica if he lets go of the Dolphin before reaching the Shipwreck.

Kingdom Hearts II
In Sora, Donald, and Goofy's second visit to Atlantica, several Dolphins dances along when the party sings "Under the Sea" along with Sebastian and Ariel.