Zidane begins the fight by himself. The Shell Dragon can use powerful physical attacks, as well as Earth Shake a strong Earth move that hits the entire party. Its Smash attack takes a party member's HP down to 1. When Zidane is forced into critical HP, by Smash or some other attack, Dagger joins the party to heal him to full health. She stays in the party for the remainder of the fight.
Shell Dragon will also appear as a random encounter throughout the remainder of Pandemonium.
When Shell Dragon is fought as a random encounter it will also use Snort to remove a random character from battle as part of its attack list. It does not use this ability in the initial fixed encounter.