One day, Mario and Luigi get a mysterious package from the Mushroom Delivery Postal Services. They open it and inside is an ancient mirror. The mirror sucks up Mario and Luigi and fuses them together to create LuigiMario!!! Then Zowzer kidnaps Princess Whatshername. Then LuigiMario goes to rescue her!!!
LuigiMario goes to Tree Town, only to be stuck at a dead end. LuigiMario has to use a Bob-omb to blow up the wall. However, LuigiMario has to go all the way to Toad Town to buy some. At Toad Town, LuigiMario gets trapped in a cage. However, with the help of Goomer, LuigiMario escapes the cage and runs to Tree Town. But at Tree Town, the wall is now made of metal. Then LuigiMario has to have a builder upgrade his Bob-ombs. Then LuigiMario uses the Metal Bob-ombs to blow up the wall. After going through a dangerous pipe system, he arrives at the Tree Castle. After going through a lot of traps and suprises, LuigiMario encounters the Tree Dragon. After defeating the Tree Dragon, LuigiMario earns the Nature Crystal.