Once again, Kirby must save the kingdom from evil. But this time he'll need some backup. As Kirby, you can call up one of four alter egos for help during your quest. Each character features new copy abilities that range from arrow-shooting to melee moves. Practice your skills in new side games, such as Crackity Hack and Speed Eaters. In addition to new abilities and subgames, Kirby & the Amazing Mirror also introduces new multiplayer modes.

There is a Mirror World that exists in the skies of Dream Land where any wish reflected in the mirror will come true. However, one day it copies the mind of a mysterious figure and creates a reflected world of evil. Meta Knight notices this and flies up to save the Mirror World.

Meanwhile, Kirby is taking a walk when Dark Meta Knight appears. Before Kirby can react, Dark Meta Knight slices Kirby in four and Kirby becomes four different colored Kirbys. They chase after Dark Meta Knight on a Warp Star simultaneously and enter the Mirror World.

It is revealed that the two Meta Knights fought each other until the real Meta Knight was defeated. He was then knocked into the mirror, which was in turn cut into eight fragments by Dark Meta Knight and scattered across the Mirror World, prompting the Kirbys to save Meta Knight and the Mirror World. After collecting all eight mirror fragments, Kirby enters the Mirror World and battles Dark Meta Knight. After defeating him, a vortex appears and sucks Kirby in, who is given Meta Knight's sword. Kirby then proceeds to fight Dark Mind, the true mastermind behind the Mirror World's corruption, multiple times. Upon defeat, the Mirror World is saved, and Shadow Kirby (the Mirror World counterpart of Kirby who is believed to be an enemy, but is now an ally) waves his goodbyes to the four Kirbys as they all exit the Mirror World one by one. Meta Knight also drops his Master sword before leaving the Mirror World, marking it as a symbol for the Mirror World's protection.