From the Super Mario Wiki
World 3-Ghost House is the Ghost House level of the third world in New Super Mario Bros. Wii. This is the first Ghost House in the game. Big Boos, smaller Boos, and possessed furniture are the main obstacles in this level. There is a platform that goes down in an area infested with Boos near the end of the level.
- Star Coin 1: At the start of the level, instead of going right, go to the left to get the hidden Star Coin.
- Star Coin 2: In the top half of the second area before reaching the top platform, you can see a lone rope on the left. Jump to it and then jump to the left to a hidden platform with the Star Coin.
- Star Coin 3: This coin can only be accessed via the secret exit. The player should keep to the right of the room with the descending platform. The Star Coin is located in a hidden area on the right wall beside the first ? Block.
Upon seeing the first yellow moving platform in the third room (shown in the picture), where the player is climbing ropes on the ceiling, they should stop and wait until it moves away. The player should then fall, landing on a hidden platform with a door. When they go into this, they will discover a platform slowly decending, with countless Boos floating around. If the player survives, a door is seen. This exit unlocks the world's warp cannon, taking the player to World 6.