The Sealion is part of the boss battle with the Black Waltz 1 in Final Fantasy IX. The battle occurs towards the end of the events in the Ice Cavern area, when the party falls asleep due to an artificial blizzard. Zidane eventually awakens and encounters Black Waltz 1, who then summons the Sealion. Both must then be defeated to win the battle. In this battle, Zidane must fight alone.
The Sealion attacks depend upon the color of the jewel on its chest, which changes as its health is depleted. When it is blue, it uses Wing or Blizzard, when it is yellow, it uses Blizzara, and when it is red, it uses Tsunami. It is difficult to kill the Sealion while the Black Waltz is still alive, as the Black Waltz will continuously heal it as soon as it is damaged. Therefore the player should take out the Black Waltz as a first priority.