Above the atmosphere is a colorful galaxy where twinkling stars illuminate small planetoids with rings resembling those of the planet Saturn. Toadette must spin upon the rings, avoid alien life forms, and uncover hidden treasures on this mysterious planet.

Toadette visits the I.N.F.E.S. Station (the Inter-National Fungi Exploration Space Station). However, the Goombas in charge have accidentally obtained some contraband cargo: a deadly and aggressive strain of alien Piranha Plant! Can Toadette make it to the escape pod with her life?

Having successfully fled the I.N.F.E.S. Station,Toadette's space journey leads her through a strangely colourful meteor stream known as Meteor Meadows where she meets the Wandering Wobbly Wigglers. But she is not the only one who managed to escape the destroyed space station: the dangerous strain of Piranha Plants is also free and begins to make its way through the wondrous Meadows.

While fleeing from the ever-growing Piranha Plant plague, Toadette spots Biscuit Bastion, Bowser Jr's intergalactic space fortress. She enters the seemingly intact stronghold, only to find the dreaded infestation already taking over its dark halls. She must find her way through deadly traps and climb the highest tower to fight Bowser Jr. before the Bastion collapses in on itself and becomes a green graveyard.

The Antigravity Armada is a legendary division in Bowser's army that not even his lowliest troops know of, and even it has been conquered by the infestation festering all over Coffee Cosmos. Will Toadette endure this ever-revolving formation, or will she succumb to the infestation as easily as the Armada did?

Toadette enters the infested space station to confront the Piranha overlord. But the space station is self-destructing! It is up to Toadette to escape the imploding station alive and stop the Piranha Plant infestation once and for all!