The best Shine for getting 100 coins in Sirena Beach will be Episode 4. There will be a few coins found outside of the hotel, so let’s concentrate on those first. At the beginning of the level, there are three crates off to your left, one of which will contain a coin (1). The torch in the middle of the plaza will spit out another coin if you spray it (2). Underneath the two huts will be an additional three coins, two under the one and a single under the vacant one (5). In front of the hotel entrance, there are eight torches, seven of which will spit out coins if you spray them. Additionally, there are two more torches on the upper ledge (14).
That’s about all the coins you’ll find outside, so speak with the Pianta in front of the hotel entrance to go inside. Once you’re in control, you will find 12 coins in the water in the lobby, four on each side of the entrance, as well as four more in the water surrounding the totem pole (26). There are ten torches in the lobby, so do the same as outside and spray them until you get a coin (36). Check behind the larger of the two stands to find two more coins, then spray the plant in the women’s bathroom for one more (39).
Head to the second floor now and find the three coins in plain sight (42). Continue to the third floor and enter the room with the pool of water. Spray the bookshelf for a single coin, then collect the ten coins in the water (53). Go towards the room with the open door to find three more coins (56). Enter that room and use the bed to reach the attic, where you will find a number of open areas that have coins. In total, you can find 18 coins in the attic from those open areas (74). Return to where you jumped up into the attic and position the camera so the Pianta cleaning is to your south.
Go to the northeast corner and Ground Pound the tile there to end up in a room with a poster. There will be four coins on the floor, plus you can get an additional two from spraying the bookshelves (80). Spray the poster in the room to create a hole, then jump into the next room to find five more coins (85). Double back to the previous room and look for the discolored tile, so Ground Pound it to end up in a room with some boxes. There will be six coins on the floor, plus five of the crates will give you a single coin (96). Head through the open doorway to find three more coins in the adjacent room (99).
That leaves you with a single coin to find for the 100-Coins Shine. You chose this particular Shine, as the casino will be open, so return to the first floor and enter it. There are little slot machines off to either side and you can Ground Pound the top of them to get coins. Most of them will give out a single coin, but some might spit out three or five coins (122). The Shine will spawn in front of the roulette wheel.