Grappling Hook

The Grappling Hook is an extremely useful item that appears in and Phantom Hourglass. It enables Link to latch on to cantilevered ledges called Grappling Posts, and use them to swing across large distances to otherwise unreachable platforms.

The Wind Waker
The Grappling Hook in is given to Link as a gift from Medli after defeating the Moblins that had captured her at the summit of Dragon Roost Cavern. A separate function of the Grappling Hook is in the stealing of enemy spoils, i.e. a Joy Pendant, a specific foe carries along with them, and the addition of those small treasures to Link's own Spoils Bag. The Grappling Hook was said to have been used by the Rito people before they obtained wings to navigate the heights and upper levels of the mountain on Dragon Roost Island.

When equipped aboard the King of Red Lions, the Grappling Hook becomes a mechanical crane, which allows Link to pull up Treasure Chests from the seabed. These sunken chests can be found beneath the clustered Light Rings scattered across the Great Sea, or by using Treasure Charts.

Phantom Hourglass
The Grappling Hook reappears in Phantom Hourglass. Here, it can be used like a Hookshot, as well as a walkable tightrope, and as a slingshot capable of blasting Link across large holes. As a Hookshot, it acts as a kilter of weight, pulling Link towards heavy objects while bringing light objects to him. As a tightrope, it also allows Link to use items while he's over it. As a slingshot, it can also redirect arrows like an Arrow Orb does, which is useful for shooting certain types of eye switches that close when Link looks at them.

The Grappling Hook is obtained in the Temple of Ice. It is used to defeat the boss, Gleeok, for which all possible ways of use will be required. The Salvage Arm replaces the Grappling Hook's crane feature at sea.

Trivia

 * This item may have helped pave the way for the Clawshot in Twilight Princess, which has some capacity of both the Grappling Hook and Hookshot. An even more comparable item, however, would be the Whip, which first appeared in Spirit Tracks with a function very much like that of the Grappling Hook in The Wind Waker, even more so than the Grappling Hook itself as it had appeared in Phantom Hourglass, the predecessor to Spirit Tracks. The Whip later went on to appear in Skyward Sword functioning even more similarly to the Grappling Hook of The Wind Waker, as it could even be used to steal treasures from certain enemies.