Kirby was traveling through a forest when he rests on a stump. The stump opens up and reveals a portal to another dimension. He jumps in. King Dedede, Meta Knight, and Bandanna Waddle Dee spy on Kirby, and jump in after him. There, the four meet Mirrorr, a mirror being that tells them that the Mirror King plans to take over the Mirror Dimension, so they go off to save the dimension!
After getting to the Mirror King's castle, they battle the Mirror King. After defeating him, it is revealed that Marx had travelled into the dimension and possessed the Mirror King. Marx battles Kirby on his own, and is eventually defeated.
Bosses and Worlds
Mirror Woods= Mirror Forest.
Kracko= Sky Palace.
Acro= Mirror Beach.
Rocky Sr.= Crystal Cave.
Mirror Army= The Mirror Kingdom.
Mirror King= Mirror King's Castle.
Marx=The Other World.
Marx Soul= The True Arena exclusive.
Ex Forms of all bosses besides Marx.
Fire, Ice, Burning, Spark, Sword, Cutter, Hammer, Parasol, Leaf, Mirror, Water, Spear, Laser, UFO, Fighter, Throw, Clean, Paint, Magic, Crash, Mike, Beam, Bomb, Missile, Wing, Ninja, Top, Cannon, Spring, Coin, Mirror Staff
Extra Mode in this game is very similar to normal Extra Modes, with Ex versions of bosses and mid bosses. Some new levels are added to certain worlds, players have halved health, and enemies are slightly different, or even changed entirely.
Mid bosses are yet to be confirmed!