The King Sepiad serves as the final boss of the Octonok Cay level. It is fought in the cove and on top of the Octonok Lighthouse. This is a guide to defeat the monster.
The first phase is more of a chase sequence than an actual boss fight. Ratchet and the gang are waterskiing with the King Sepiad in pursuit. The king has three attacks: sweeping his tentacles across the screen, tossing a ship, and biting from below. The bite attack is telegraphed by bubbles that appear. To damage the boss, the gang must activate the three shock towers in the cove. Rotate the Left analog stick to activate the tower and electrocute the King Sepiad. After activating all three towers, the King will fall into the sea, appearing to be dead.
The King Sepiad is thought to be dead, but later attacks the gang as they climb the Lighthouse. The true fight begins when they reach the top. The King again attacks by slapping the ground with its tentacles. Easily avoided, provided you're not under them. To damage the boss, the gang must push Slorgs into the center of the arena, easily done with the Critter Strike. Once enough Slorgs have been pushed in, a verse-crank will appear. Turn the crank to activate the lighthouse beacon. This will daze the Sepaid, allowing the gang to damage him. First, use the Vac-U to pull on the tag on its lower jaw. Then, push Slorgs into its mouth. This will elctrocute him. Keep pushing Slorgs in until he snaps out of his trance. You must again push Slorgs into the center of the arena to bring out the versa-crank, but the boss covers it with a tentacle. Fire a few shots at the tentacle to force him to let go, and activate the crank to turn on the beacon and again stun him. Feed him a few Slorgs until he starts to choke. He will then fall over, allowing the gang to finish him off with whatever weapon in your arsenal.