Nimbus Land is a kingdom far above Mushroom Kingdom. The only way to get to it is to use trampolines.
Mario's partner, Mallow, is the lost prince of the Nimbus Land, he was lost as a child and taken care of the tadpoles and Frogfucious. Taking advantage of the fact that the people had no idea where Mallow was, Valentina claimed she had found the lost prince. She then takes her rule of Nimbus Land pretending to use "Mallow's" word to rule. Mario and Mallow get there just as Valentina is tricking all of Nimbus Land, and they manage to stop her after having to fight Birdo, Dodo, and herself. Mallow finally finds out where he is from, and he meets his parents, and regains his rightful title as the Prince of Nimbus Land.
After beating Valentina and Dodo, Mario and Mallow had to continue on their journey to find the seven stars. Mallow's parents, the king and queen of Nimbus Land, told them that there is a star in Barrel Volcano, but the dangerous Czar Dragon lives there. Mario and his party ventured the volcano, beat the Czar Dragon, they had thought they were victorious, but then out of the ashes rose Zombone. Mario and his party had another tough battle ahead of them, but once again they triumphed and retrieved the star.