Hydraxus is Captain Mareed's guardian.
It is a giant blue rock squid, that can only be summoned in water. It has three red eyes, mandibles besides its mouth, and hooked rocks at the end of its tentacles.
It attacks its enemies with its tentacles, or Depth Charge, which creates a water-tornado that is powerful enough to destroy guardians. Its massive size can create waves, to rock over ships beside it.
- It appears as an enemy guardian in the DS game. It uses Ogama and Yan attacks.