Piko Piko Hammer

The Piko Piko Hammer (ピコピコハンマー) is Amy Rose's signature magical hammer. She uses it to crush her enemies and its power is capable of making tornadoes and huge shockwaves.

Size
Amy's hammer varies in size. It can be as small as her head, or it can be larger than her body. One of its larger sizes was shown in Sonic X Episode 9 where Dr. Eggman destroyed a bracelet she made as a gift for Sonic. In a fit of unbelievable rage, she whipped out the hammer and flattened one of Eggman's giant robots in a parody of the ancient Japanese game, Daruma Otoshi, and sent Eggman flying into the ocean. In Sonic & Sega All-Stars Racing, Amy's All Star move has her take out the Piko Piko Hammer, with it being the size of her car.

Other characters
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 the game Tails Adventure.

Also, in the game Sonic Advance 3, when selecting Amy as the leader or the sidekick, her partner will also have a Piko Piko Hammer (it does not matter which character is chosen as Amy's partner).

Trivia

 * Some say her hammer looks like Luigi's Sqeaky Mallet in Mario Power Tennis\Power Tour and also both of their hammers are called "toy hammer" in Japan.
 * No one actually knows how she is able to magically pull out her hammer. This fact was even parodied in Sonic X and her profile in Super Smash Bros. Brawl.
 * She also seems to have an inexhaustible supply of Piko Piko Hammers, as proven by Episode 52 of Sonic X where she conjured up a Piko Piko Hammer out of nowhere just by waving her hand. Decoe made fun of this by saying that Amy had a "whole warehouse full" of hammers.
 * Amy seems to have some sort of connection to her hammers, because in the Sonic X comic when she, Sonic, Knuckles, Tails and Rouge are trapped in a virtual reality by Eggman, Amy says she can't 'feel' her hammer while she's within the illusion.
 * In Sonic the Fighters, Amy's hammer isn't referred to as the "Piko Piko Hammer" but the "Magical Hammer".
 * The hammer isn't indestructible, however. In the Archie comics, Amy's anti-self managed to break a normal-sized hammer (not a giant one) with her own version of the Piko Piko Hammer.
 * In some games, the hammer can be used to hit Springs, causing her to catapult quite a bit further, and can be used like a spring in Sonic Adventure and sometimes in the Sonic Advance games.
 * In Sonic Adventure, a much stronger version of the Piko Piko Hammer is the Long Hammer. Of which that was obtained from the Egg Carrier (destroyed) if Amy beats her "own" score she set after beating Eggman's 2000pt score in "his" version of the Whac-A-Mole minigame in Story Mode.
 * It is possible that Amy has different "versions" of Piko-Piko Hammers. As seen in Sonic Heroes, as she uses the Air Hammer which utilizes the power of the wind and her normal red and yellow hammers.