After Valentina runs away from you in Nimbus Castle, you catch up with her in Nimbus Land.

Dodo

At the start of the battle, Dodo will carry off one of your party members and battle one-on-one with them. You just need to deal about 200 HP to make Dodo run away.

Valentina

After Dodo runs away, your other two party members will need to battle Valentina. She can use many of the magic attacks you have seen thus far, (e.g. Water Blast, Blizzard, Petal Blast, Drain Beam, and many more) as well as regular attacks.

Valentina and Dodo

After you deal enough damage, Dodo will come back, and your other party member will return to the battle. Dodo is weak to Fire.

After the Battle

There will be a cutscene after the battle, and you will learn your next destination. Before you go, you should exit the castle by going northwest from this room. Hit the chest on the way, and this time it contains a Flower. Go northeast until you fall down next to the smiley spring, and jump on it, then jump onto the next smiley spring. From there, go east the the southeast edge of Nimbus Land, and run northward while pushing against the southeast edge, until you find a hidden path. Go southeast along this hidden path to find the Shy Away from earlier. Talk to it to get Fertilizer.

Fall through the hole in Nimbus Land to go back to the two springs, and jump onto the eastern spring to return to the World Map. Go all the way back to Rose Town, and go to the northeast part of town to find a new exit, which leads to the gardener's house. Talk to the Gardener and agree to give him the Seed and the Fertilizer. After the cutscene, go outside and jump up the boxes to reach the beanstalk. Touch it to climb up. Hit the chest to get Mario's best weapon, the Lazy Shell, and an armor that all characters can wear, which is also known as the Lazy Shell. The armor greatly increases defense and magic defense, at the expense of attack and magic attack, which are greatly reduced.

Moving On

When you're ready to continue, go to the entrance of Nimbus Land. Fall down the northeast hole to go where the two guards are blocking the entrance to the hot springs. Talk to them and there will be a cutscene. Go southeast to enter the hot springs. You can jump into the hot springs to fully heal up. You can optionally read the note to the right of the hot springs. Then go southeast to jump into Barrel Volcano.