Plesiosaur

Modeled on the real prehistoric reptile it shares a name with, this monster carries a humped torso, four broad flippers, and a long, supple neck. Its mouth opens wide enough to gulp down a grown person in a single bite. The one ornament it wears is a plated kabuto helmet stamped with the Ganzack Pirates' Jolly Roger and trimmed with crab claws.

Savage and quick to attack, the creature is nonetheless sharp enough to follow Ganzack's commands, including ferrying targets like Nami to him without harming them. It also has the sense to flinch when it spots dynamite, recognizing the threat for what it is.

The beast swims with tremendous force, big enough to splinter small craft just by surfacing and powerful enough to haul Ganzack's warship along without apparent effort. Its flexible neck lets it pluck foes out of the air on its fangs, though its jaws cannot quite pin down the rubbery Luffy.

Exactly when or how Ganzack captured and trained the monster is never explained, though it likely happened around the time his crew overran Medaka's home island. Afterward it lived mostly in an undersea cavern, sent out now and then to patrol and hunt. On one such circuit it ran into the famished Straw Hats and wrecked their boat, shrugging off Luffy and Zoro before delivering Nami to Ganzack. When the crew later allied with the island's rebels, Ganzack had the beast tow out his great cannon and warship to shell the island from a distance. The defenders and Nami answered with a small fireship packed with dynamite, dragging both the monster and the warship down to the bottom.