kirby & the amazing mirror
The first mainline Kirby game on the Game Boy Advance, and the second GBA Kirby game overall after Nightmare in Dream Land. It introduces four-player co-op to the series and appears to try to combine the slower pace of Kirby's Adventure with the varied movesets of copy abilities ala Kirby Super Star.
High above Dream Land, there is a dimension mirror that acts as a portal to the Mirror World. One day, the Mirror World is attacked by a dark force and Meta Knight sets out to investigate.
Meanwhile, Kirby is out strolling in the spring breeze when Dark Meta Knight suddenly attacks him, splitting him into four. Confused, Kirby and his new clones follow the attacker to the Mirror World.