Gyorm

Gyorm are strange fish-like enemies that appear in. They hover around the Swamp Palace in unusual spiked shells. These shells are both a form of locomotion and defense, as a Gyorm cannot be harmed while hiding within. They are not particularly aggressive, but they will cause harm to Link if they come into contact with him. To defeat a Gyorm, they must be pulled from their shells using the Hookshot. Once dragged from the safety of their shell, they are far less mobile, and vulnerable to the Master Sword. They will attempt to return to their shell, and must be defeated before they can.

Gyorm hover over water rather than swim in it, and may not actually be aquatic at all, as dragging them out into deep water will cause them to drop in and be defeated.