There are several Invisible Blocks near the start of the level. Each one contains a Super Star. When you see a cluster of four coins, hit the space in the middle to reveal an Invisible Block.
The first Star Coin is above the platform at Point 2. There’s a Red Spike Buzzy patrolling the platform—grab the Super Star from the nearby Invisible Block to ensure you clear out the enemy on your way to the Star Coin.
The second Star Coin is floating below the platform at Point 3. To collect it, stomp the nearby Buzzy Beetle and throw its shell at the Block to the right. After a few bounces, the shell passes through the Star Coin.
The third Star Coin is floating above the Red Spike Buzzies at Point 4. Clear the enemies from the nearby platform, then jump across to collect the Star Coin.