- Star Coin 1: When entering the underwater world through the pipe, turn left and follow the pipe current to the Star Coin.
- Star Coin 2: After the trail of the eight red-coins, go between the gap of the yellow pipes above where the second Star Coin will be revealed.
- Star Coin 3: At the same gap, swim upward to a hidden area above water where the third Star Coin is.
Hidden Luigi image
On the right side of the yellow pipe that blocks the entry to the finish shows a picture of standard Luigi swimming from Super Mario Bros.