Upon exiting the room with Itoh you will find yourself in the Plantation. This map is quite large and there is a lot to do here.
Immediately above you there is a path going up through the rock which you can go up through a series of jumps or fly, it leads to an unidentified path which leads to a room full of statues. The statues do not yet serve a purpose, but show the previous rulers of the island.
Immediately down you will find a similar jump path boring down into the side of the mountain. If you saved Curly and successfully drained her of water, you will find her bedridden at the bottom room, next to a creature who found her. Speak to the creature, then to Curly, then to the creature again to find out that Curly has lost all her memory and that the cure is to eat a special mushroom. If you want the best ending you must find and feed her this mushroom before leaving for the Final Cave.
To save several tedious trips through the outer wall and now destroyed egg corridor, you should probably first find one of the two teleporters in the plantation before proceeding to procure a cure for Curly.
Go back to the now abandoned Mimiga Village, enter the graveyard, at the top right there is a door that was previously unreachable, fly up there and you will find a mushroom called Ma Pignon. Talk to him and he will ask if you are sure you want the mushroom badge, you will have to say yes every time he asks if you want it, and say no every time he asks if you don't want it, eventually you will get the Mushroom Badge. Do NOT leave yet. You must now go into the inventory and examine the Mushroom Badge, this will reveal it to be a useless trinket. Go back to Ma Pignon, he will laugh at you for buying into the whole badge thing.
After a short dialogue he will ask if you really want to eat him. Say yes to start the battle with him. After defeating him you get him in your inventory and can feed him to Curly to cure her amnesia. Go back to Curly, shove Ma Pignon in her mouth, and watch as she regains all memory, even memories from before you met her. Talk to her again to get the Iron Bond item.
Far to the left you will find a prison full of Mimigas, you can talk to them for hints and clues. There is a secret tunnel at the left top part of the prison; it leads to a teleporter which leads to the grasslands, the teleporter in the grasslands is now active and can be used to teleport back to the plantation.
Here you will find the fisherman, spare sprinklers, and resting Mimigas. Talk to the fisherman to get him to go fishing. Most Mimigas will not talk to Humans.
At the bottom part of the level there is a long stretch of water. Advancing left takes you to the locked door to the Teleporter Room. To access the room, you must go to the Break Room and talk to the fishing Mimiga, who will fish out the key out of an instant death trap for you. Go in the teleporter inside the now unlocked room..
When you try teleporting for the first time you will be knocked out and put in prison, this will advance the plot.
Talk to the Mimiga imprisoned with you twice. Check your inventory, read the letter from Sue. This will open up the tunnel in the back of the prison allowing you to escape, and provide you with the password for the Hideout, where Sue's mother is working against the Doctor. The hideout is southwest of the entrance to the Plantation, accessed by going through a small hidden tunnel next to the door.
You will temporarily lose your Booster after talking to Sue's mother. Don't worry, while it sounds like the loss is permanent, you get it back in short order. Sue's mother gives you a Mimiga mask and asks for a sprinkler. Go all the way left and find a broken sprinkler, take it back to rest area, talk to the guy watching over the new sprinklers, and he will swap with you. Take the new sprinkler to Sue's mother.
She now needs Itoh's help, go all the way to the right to where you entered the plantation originally, find Itoh, he will give you a Controller for Sue's mother. She will use it to finish the rocket which will allow you to progress to the next level. Sleep, then talk to her to get back your Booster. You don't have to fly up yet, and you can safely fall down and pass by the death traps.