Hover over the icons under "Damage" to see list of attacks.
Strategy: Use Petroleum or a trained Pirate against Seashell. After Seashell is defeated, 2 Cool Fires are ideal, as they are resistant/immune against all the elemental attacks from Dragonfly and Steampunk. In doubt, as usual, use Legends or Pures for any of these battles... (standard Pure is *very* effective against Steampunk)
At minimum, your dragons should be level 15.