Trident

The Trident is a sacred relic that gives it's wielder the ability to control the sea, or Atlantica. It is more of a spellcasting weapon then a melee weapon. King Triton is the current wielder of the Trident.

Powers
Its main power is shooting a large blast of yellow energy at a certain target. Other powers it has, examples have shown, are manipulating water and changing the present state of a being. In Kingdom Hearts II, King Triton uses it to write his name on a contract. When wielding the Trident, Ursula uses some thunder and blizzard-type attacks during the second boss battle against her, but it is not certain that all these attacks were the power of the trident.

Kingdom Hearts
In Kingdom Hearts, Triton is still the wielder of the trident. He uses its power to destroy a few Screwdivers in one instance, and then to destroy a crystal trident, that is the key to Atlantica's keyhole. Ursula eventually steals it again and, like the movie, grows to a gigantic size. Sora and co. defeat her and then use the trident as a replacement for the trident crystal to seal the keyhole.

Kingdom Hearts II
In Kingdom Hearts II, the trident only appears in scenes with Triton and the end song-battle against Ursula, where she uses it as a weapon again.

Etmology
A trident is the royal sceptor of Poseidon and Triton in greek mythology.