The Piko Piko Hammer (ピコピコハンマー, PikoPiko Hanmā) is Amy Rose's signature weapon. She uses it to crush her enemies and its power is capable of making tornadoes and huge shockwaves.
First appearing with the pink hedgehog in Sonic the Fighters as the "Magical Hammer", Amy's mallet is a destructive force that fills even Sonic with dread (Sonic X, Sonic Riders). How Amy manages to carry the massive thing around and whip it out at a moment's notice is a mystery, occasionally played with for comic effect (Sonic X, Amy's Brawl profile).
While Amy is capable of pulling off the spin attack in some games, usually she relies on her hammer as a means of subduing enemies. It can also be used to catapult her further off springs in Sonic Advance. In both Sonic Heroes and Sonic Battle Amy can use the weapon to generate a cyclone with the moves Tornado Hammer and Pink Typhoon.
In Sonic & Sega All-Stars Racing, Amy's All-Star move gives her a gigantic Piko hammer which she can use on the other racers.
The Long Hammer is an upgraded version of the Piko Piko Hammer in Sonic Adventure, available for Amy to acquire for beating her high score in the Whack-a-mole game within the Egg Carrier Adventure Field.
Although the Piko Piko Hammer is best known as Amy's signature weapon, various other characters have used hammers as well. Tails uses a hammer in Tails Adventure. Also, in Sonic Advance 3, when selecting Amy as either leader or sidekick, her partner will also have a Piko Piko Hammer.
Some of Amy's various hammer-based moves: