New Super Luigi U: Meringue Clouds-6 -- Three-Headed Snake Block

As the title suggests, the snake block in this level will split into three early on. This is an automatic sidescroller. Beware of the Foos and the fog they create. You can spin to clear it up. Stay on the bottom snake block for the first Star Coin. Get an Acorn and you'll find the second Star Coin hidden in a cloud near the top past the Red Coins. The third Star Coin is nearby, towards the top. The snake blocks will take you to the flag.