Episode 3: Mysterious Hotel Delfino
This mission marks the first time in Sirena Beach that Yoshi appears. However, he will only accept pineapples. The fruit stand, unfortunately, does not have any pineapples.
You can take the stairs all the way up to the top floor of the hotel, but you won't get far since the path to the Shine (through the ventilation-shaft-like fourth floor) is blocked by Giant Boos that Mario can't defeat without Yoshi's help. To get to the pineapple, you must skip the stairs and find a new route. Head to the men's bathroom in the first floor (on the far left corner if you are coming from the entrance), and go to the stall at the end. When you see the leaky toilet, jump into it, and you will come out in a second floor bathtub.
For the rest of this mission, the doors should be avoided. They will just send you back out to the lobby, and lock behind you. Instead, make your own doors: In this room, spray the painting until it reveals a Boo, and jump through it to a room with some Noki children and a bunch of Boos.
Defeat the Boos, then spray the four thatch panels until they form the image of a Boo; a path to a new room opens. This room is full of Pink Boos, which you can turn into platforms and use to hover through a hole in the ceiling.
In the first room of the third floor, you can spray the left of the two bookcases for the first of seven Blue Coins in this Episode, and then spray the empty shelves to make a passage to the next room. In that room, you can soak the Dolphic poster to open a passage to a room with another Blue Coin. To progress in your quest, find the lightest floor panel in the room with the Dolphic poster, and give it a good ground pound. The panel will break, dropping you into a room with a bunch of crates full of pineapples! Grab one, head out the door and head downstairs to Yoshi.
If your going after Blue Coins as well, you must repeat the entire loop with Yoshi (starting in the men's room and ending in the pineapple room), so you can have Yoshi eat the Big Boo in the pineapple room, allowing you to access a small room with a Blue Coin. If you don't care, simply take Yoshi up to the third floor via the stairs.
There is one open door on the third floor, which leads to a room with some Nokis and a big fluffy bed. Jump off the bed and into a ventilation shaft, and you will end up in the hotel's maze-like fourth floor. Yoshi's job is to eat all the Big Boos, but there is plenty of coins to grab on the way. There are even two Blue Coins, but only one of them is real. As you search this floor, note the cracks on the ground, but don't ground pound them yet. They lead to some Blue Coins and the Shine, but it's not anywhere you want to go with Yoshi. Use him to clear out all the Big Boos, then leave him behind.
There are four cracks you can ground pound. The one in the middle of the fourth floor leads to the third floor lobby area, and the one in the corner down the hall (on the right-hand side of the Pianta sweeper) leads to the room with the Dolphic poster. Skip these two, and instead head down the passage to the sweeper's left. Make a left turn at the four-way intersection, and pass the left turn that leads to the real Blue Coin. If you want to get the Shine, take the next left, and ground pound the crack in the room at the end of that shaft. If you want to find the final two Blue Coins in this Episode, skip that last left turn and ground pound the crack in the room you will get to if you go straight instead.