Ice Rod

From Zelda Wiki.org

Appearing exclusively in A Link to the Past, this blue rod harnesses the power of ice. Link can find this weapon in a cave to the east of Lake Hylia, but the cave cannot be opened without a bomb. Because, bombs can be purchased very early in the game, Link can get this legendary weapon even before entering the first dungeon. By using a little magic power, Link can use this to shoot a snow-like projectile. Most enemies will be permanently frozen solid if they are hit, but some will be defeated instantly. The Ether Medallion's effect will often have a similar result on enemies.

The Ice Rod is particularly effective against the Lanmolas boss, as one shot can dish out enough damage as four normal sword swings.