The history of the Ghost Toads, from the manual:
In the Dark Bloo Inn, a Ghost Toad can be found in the library. He throws the books off of the shelves when Mario first enters. He appears when Mario paints him, and he tells him that he is searching for a book. He tells Mario that someone probably took it and did not return it. After Mario obtains the book from a Toad and returns it to the Ghost Toad, the Ghost Toad heads to the dining hall, where the tea party takes place.
Another Ghost Toad can be found pushing a luggage cart on the second floor. When Mario causes him to appear by painting him, he says that he cannot find Room 201. After Mario uses the Cutout ability to remove the wall blocking the door, talking to the Ghost Toad again will cause Huey to point out Room 201, and he runs over to it. After he puts his luggage in the room, he heads down to the tea party.
A Ghost Toad can be found in Room 202, though the room can only be entered by going through a hole in the floor of Room 302. He appears when Mario paints the area near the table. He will be on the floor trying to find his glasses, which are on his head. If Mario hits him with his hammer, the glasses will go back onto his face. He will then go down to the tea party. If Mario does not break the crate in front of the door, the Ghost Toad will break it by running into it. This will cause his glasses to go onto his head again, though he will put them back on immediately after.
When Mario enters Room 203, a Shy Guy can be seen jumping off a balcony, carrying something invisible. By painting the area near the balcony, a Ghost Toad can be found banging on the rail, saying that the Shy Guy stole "it." After Mario obtains "it" from a Shady Sledge Bro and returns it to the Ghost Toad, he puts it on the table and heads down to the tea party.
When Mario enters Room 301, the furniture can be seen scattered everywhere. The house cleaning Toad will come in and clean the room, and, when he leaves the room, Mario can find a Ghost Toad talking on a telephone. He becomes angered that the hotel is not changing his sheets, and threatens to mess up the room again. After Mario obtains the Fresh Sheets from Shy Guys, he must go to Room 301 and change the old sheets out for the fresh sheets, causing the Ghost Toad to become happy. He then goes down to his tea party.
In Room 303, a Ghost Toad can be found near a colorless birdcage. He says that his "red bird" has escaped. After Mario paints and picks up the birdcage and finds the "red bird", a Koopa Paratroopa, outside, he takes it to the Ghost Toad. The Ghost Toad then heads down to the tea party.
The Ghost Toads can be found in the dining hall, though their teapot is missing. They begin to get annoyed that they cannot have their tea party yet.
When Mario gets the Teapot from Plum Park, he can give it to the Ghost Toads. The Ghost Toads then finally are able to have their tea party, and they rise into the sky. Their pictures then appear in the painting behind the table. Mario receives an extra card slot for helping the Ghost Toads.